Browsing by Subject "galaxies: ism"
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Item Circumnuclear Molecular Gas In Megamaser Disk Galaxies NGC 4388 And NGC 1194(2014-06) Greene, Jenny E.; Seth, Anil; Lyubenova, Mariya; Walsh, Jonelle; van de Ven, Glenn; Lasker, Ronald; Walsh, JonelleWe explore the warm molecular and ionized gas in the centers of two megamaser disk galaxies using K-band spectroscopy. Our ultimate goal is to determine how gas is funneled onto the accretion disk, here traced by megamaser spots on sub-parsec scales. We present NIR IFU data with a resolution of similar to 50 pc for two galaxies: NGC 4388 with VLT/SINFONI and NGC 1194 with Keck/OSIRIS+AO. The high spatial resolution and rich spectral diagnostics allow us to study both the stellar and gas kinematics as well as gas excitation on scales only an order of magnitude larger than the maser disk. We find a drop in the stellar velocity dispersion in the inner similar to 100 pc of NGC 4388, a common signature of a dynamically cold central component seen in many active nuclei. We also see evidence for noncircular gas motions in the molecular hydrogen on similar scales, with the gas kinematics on 100 parsec scales aligned with the megamaser disk. In contrast, the high ionization lines and Br gamma trace outflow along the 100 parsec-scale jet. In NGC 1194, the continuum from the accreting black hole is very strong, making it difficult to measure robust two-dimensional kinematics, but the spatial distribution and line ratios of the molecular hydrogen and Br gamma have consistent properties between the two galaxies.Item Cold Dust but Warm Gas in the Unusual Elliptical Galaxy NGC 4125(2013-10) Wilson, C. D.; Cridland, A.; Foyle, K.; Parkin, T. J.; Cooper, E. Mentuch; Roussel, H.; Sauvage, M.; Smith, M. W. L.; Baes, M.; Bendo, G.; Boquien, M.; Boselli, A.; Ciesla, L.; Clements, D. L.; Cooray, A.; De Looze, I.; Galametz, M.; Gear, W.; Lebouteiller, V.; Madden, S.; Pereira-Santaella, M.; Remy-Ruyer, A.; Cooper, E. MentuchData from the Herschel Space Observatory have revealed an unusual elliptical galaxy, NGC 4125, which has strong and extended submillimeter emission from cold dust but only very strict upper limits to its CO and Hi emission. Depending on the dust emissivity, the total dust mass is 2-5 x 10(6) M-circle dot. While the neutral gas-to-dust mass ratio is extremely low (<12-30), including the ionized gas traced by [CII] emission raises this limit to <39-100. The dust emission follows a similar r(1/4) profile to the stellar light and the dust to stellar mass ratio is toward the high end of what is found in nearby elliptical galaxies. We suggest that NGC 4125 is currently in an unusual phase where evolved stars produced in a merger-triggered burst of star Formation are pumping large amounts of gas and dust into the interstellar medium. In this scenario, the low neutral gas-to-dust mass ratio is explained by the gas being heated to temperatures >= 10(4) K faster than the dust is evaporated. If galaxies like NGC 4125, where the far-infrared emission does not trace neutral gas in the usual manner, are common at higher redshift, this could have significant implications for our understanding of high redshift galaxies and galaxy evolution.Item Continuum Observations At 350 Microns Of High-Redshift Molecular Emission Line Galaxies(2009-12) Wu, Jingwen Wu; Vanden Bout, Paul A.; Evans, Neal J.; Dunham, Michael M.; Wu, Jingwen Wu; Evans, Neal J.; Dunham, Michael M.We report observations of 15 high-redshift (z = 1-5) galaxies at 350 mu m using the Caltech Submillimeter Observatory and Submillimeter High Angular Resolution Camera II array detector. Emission was detected from eight galaxies, for which far-infrared luminosities, star formation rates (SFRs), total dust masses, and minimum source size estimates are derived. These galaxies have SFRs and star formation efficiencies comparable to other high-redshift molecular emission line galaxies. The results are used to test the idea that star formation in these galaxies occurs in a large number of basic units, the units being similar to star-forming clumps in the Milky Way. The luminosity of these extreme galaxies can be reproduced in a simple model with (0.9-30) x10(6) dense clumps, each with a luminosity of 5 x 10(5) L(circle dot), the mean value for such clumps in the Milky Way. Radiative transfer models of such clumps can provide reasonable matches to the overall spectral energy distributions (SEDs) of the galaxies. They indicate that the individual clumps are quite opaque in the far-infrared. Luminosity-to-mass ratios vary over two orders of magnitude, correlating strongly with the dust temperature derived from simple fits to the SED. The gas masses derived from the dust modeling are in remarkable agreement with those from CO luminosities, suggesting that the assumptions going into both calculations are reasonable.Item Demographics of Bulge Types Within 11 Mpc and Implications for Galaxy Evolution(2011-06) Fisher, David B.; Drory, Niv; Fisher, David B.We present an inventory of galaxy bulge types (elliptical galaxy, classical bulge, pseudobulge, and bulgeless galaxy) in a volume-limited sample within the local 11 Mpc sphere using Spitzer 3.6 mu m and Hubble Space Telescope data. We find that whether counting by number, star Formation rate, or stellar mass, the dominant galaxy type in the local universe has pure disk characteristics (either hosting a pseudobulge or being bulgeless). Galaxies that contain either a pseudobulge or no bulge combine to account for over 80% of the number of galaxies above a stellar mass of 10(9) M-circle dot. Classical bulges and elliptical galaxies account for similar to 1/4, and disks for similar to 3/4 of the stellar mass in the local 11 Mpc. About 2/3 of all star Formation in the local volume takes place in galaxies with pseudobulges. Looking at the fraction of galaxies with different bulge types as a function of stellarmass, we find that the frequency of classical bulges strongly increases with stellar mass, and comes to dominate above 10(10.5) M-circle dot. Galaxies with pseudobulges dominate at 10(9.5)-10(10.5) M-circle dot. Yet lower-mass galaxies are most likely to be bulgeless. If pseudobulges are not a product of mergers, then the frequency of pseudobulges in the local universe poses a challenge for galaxy evolution models.Item Extreme Gas Fractions in Clumpy, Turbulent Disk Galaxies at Z Similar To 0.1(2014-08) Fisher, David B.; Glazebrook, Karl; Bolatto, Alberto; Obreschkow, Danail; Cooper, Erin Mentuch; Wisnioski, Emily; Bassett, Robert; Abraham, Roberto G.; Damjanov, Ivana; Green, Andy; McGregor, Peter; Cooper, Erin MentuchIn this Letter, we report the discovery of CO fluxes, suggesting very high gas fractions in three disk galaxies seen in the nearby universe (z similar to 0.1). These galaxies were investigated as part of the DYnamics of Newly Assembled Massive Objects (DYNAMO) survey. High-resolution Hubble Space Telescope imaging of these objects reveals the presence of large star forming clumps in the bodies of the galaxies, while spatially resolved spectroscopy of redshifted II alpha reveals the presence of high dispersion rotating disks. The internal dynamical state of these galaxies resembles that of disk systems seen at much higher redshifts (1 < z < 3). Using CO(1-0) observations made with the Plateau de Bure Interferometer, we find gas fractions of 20%-30% and depletion times of t(dep) similar to 0.5 Gyr (assuming aMilky-Way-like alpha(CO)). These properties are unlike those expected for low-redshift galaxies of comparable specific star Formation rate, but they are normal for their high-z counterparts. DYNAMO galaxies break the degeneracy between gas fraction and redshift, and we show that the depletion time per specific star Formation rate for galaxies is closely tied to gas fraction, independent of redshift. We also show that the gas dynamics of two of our local targets corresponds to those expected from unstable disks, again resembling the dynamics of high-z disks. These results provide evidence that DYNAMO galaxies are local analogs to the clumpy, turbulent disks, which are often found at high redshift.Item The Gould Belt "Misfits" Survey: The Real Solar Neighborhood Protostars(2015-06) Heiderman, Amanda; Evans, Neal J.; Evans, Neal J.We present an HCO+ J = 3. 2 survey of Class 0+I and Flat SED young stellar objects (YSOs) found in the Gould Belt clouds by surveys with Spitzer. Our goal is to provide a uniform Stage 0+I source indicator for these embedded protostar candidates. We made single point HCO+J = 3 -> 2 measurements toward the source positions at the CSO and APEX of 546 YSOs (89% of the Class 0+I +Flat SED sample). Using the criteria from van Kempen et al., we classify sources as Stage 0+I or bona fide protostars and find that 84% of detected sources meet the criteria. We recommend a timescale for the evolution of Stage 0+I (embedded protostars) of 0.54 Myr. We find significant correlations of HCO+integrated intensity with a and Tbol but not with Lbol. The detection fraction increases smoothly as a function of a and Lbol, while decreasing smoothly with Tbol. Using the Stage 0+I sources tightens the relation between protostars and high extinction regions of the cloud; 89% of Stage I sources lie in regions with A(V) > 8 mag. Class 0+I and Flat SED YSOs that are not detected in HCO+ have, on average, a factor of similar to 2 higher Tbol and a factor of similar to 5 lower L-bol than YSOs with HCO+ detections. We find less YSO contamination, defined as the number of undetected YSOs divided by the total number surveyed, for sources with T-bol less than or similar to 600 K and L-bol greater than or similar to 1 L-circle dot. The contamination percentage is > 90% at A(V) < 4 mag and decreases as A(V) increases.Item The Herschel Exploitation Of Local Galaxy Andromeda (HELGA). II. Dust And Gas In Andromeda(2012-09) Smith, Mathew W. L.; Eales, Steve A.; Gomez, H. L.; Roman-Duval, J.; Fritz, J.; Braun, R.; Baes, Maarten; Bendo, George J.; Blommaert, Jadl; Boquien, Mederic; Boselli, Alessandro; Clements, D. L.; Cooray, Asantha R.; Cortese, L.; de Looze, I.; Ford, G. P.; Gear, W. K.; Gentile, G.; Gordon, K. D.; Kirk, J.; Lebouteiller, Vianney; Madden, S.; Mentuch, E.; O'Halloran, B.; Page, M. J.; Schulz, B.; Spinoglio, L.; Verstappen, J.; Wilson, Christine D.; Thilker, D. A.; Mentuch, E.We present an analysis of the dust and gas in Andromeda, using Herschel images sampling the entire far-infrared peak. We fit a modified-blackbody model to similar to 4000 quasi-independent pixels with spatial resolution of similar to 140 pc and find that a variable dust-emissivity index (beta) is required to fit the data. We find no significant long-wavelength excess above this model, suggesting there is no cold dust component. We show that the gas-to-dust ratio varies radially, increasing from similar to 20 in the center to similar to 70 in the star-forming ring at 10 kpc, consistent with the metallicity gradient. In the 10 kpc ring the average beta is similar to 1.9, in good agreement with values determined for the Milky Way (MW). However, in contrast to the MW, we find significant radial variations in beta, which increases from 1.9 at 10 kpc to similar to 2.5 at a radius of 3.1 kpc and then decreases to 1.7 in the center. The dust temperature is fairly constant in the 10 kpc ring (ranging from 17 to 20 K), but increases strongly in the bulge to similar to 30 K. Within 3.1 kpc we find the dust temperature is highly correlated with the 3.6 mu m flux, suggesting the general stellar population in the bulge is the dominant source of dust heating there. At larger radii, there is a weak correlation between the star formation rate and dust temperature. We find no evidence for "dark gas" in M31 in contrast to recent results for the MW. Finally, we obtained an estimate of the CO X-factor by minimizing the dispersion in the gas-to-dust ratio, obtaining a value of (1.9 +/- 0.4) x 10(20) cm(-2) [K km s(-1)](-1).Item The HETDEX Pilot Survey. II. The Evolution Of The Ly Alpha Escape Fraction From The Ultraviolet Slope And Luminosity Function Of 1.9 < Z < 3.8 Laes(2011-07) Blanc, Guillermo A.; Adams, Joshua J.; Gebhardt, Karl; Hill, Gary J.; Drory, Niv; Hao, Lei; Bender, Ralf; Ciardullo, Robin; Finkelstein, Steven L.; Fry, Alexander B.; Gawiser, Eric; Gronwall, Caryl; Hopp, Ulrich; Jeong, Donghui; Kelzenberg, Ralf; Komatsu, Eiichiro; MacQueen, Phillip; Murphy, Jeremy D.; Roth, Martin M.; Schneider, Donald P.; Tufts, Joseph; Blanc, Guillermo A.; Adams, Joshua J.; Gebhardt, Karl; Hill, Gary J.; Fry, Alexander B.; |Jeong, Donghui; Komatsu, Eiichiro; Murphy, Jeremy D.We study the escape of Ly alpha photons from Ly alpha emitting galaxies (LAEs) and the overall galaxy population using a sample of 99 LAEs at 1.9 < z < 3.8 detected through integral-field spectroscopy of blank fields by The Hobby Eberly Telescope Dark Energy Experiment Pilot Survey. For 89 LAEs with broadband counterparts we measure ultraviolet (UV) luminosities and UV slopes, and estimate E(B - V) under the assumption of a constant intrinsic UV slope for LAEs. These quantities are used to estimate dust-corrected star formation rates (SFRs). Comparison between the observed Ly alpha luminosity and that predicted by the dust-corrected SFR yields the Ly alpha escape fraction. We also measure the Ly alpha luminosity function and luminosity density (rho(Ly alpha)) at 2 < z < 4. Using this and other measurements from the literature at 0.3 < z < 7.7 we trace the redshift evolution of rho(Ly alpha). We compare it to the expectations from the star formation history of the universe and characterize the evolution of the Ly alpha escape fraction of galaxies. LAEs at 2 < z < 4 selected down to a luminosity limit of L(Ly alpha) > (3-6) x 10(42) erg s(-1) (0.25-0.5 L*), have a mean < E(B - V)> = 0.13 +/- 0.01, implying an attenuation of similar to 70% in the UV. They show a median UV uncorrected SFR = 11 M-circle dot yr(-1), dust-corrected SFR = 34 M-circle dot yr(-1), and Ly alpha equivalent widths (EWs) which are consistent with normal stellar populations. We measure a median Ly alpha escape fraction of 29%, with a large scatter and values ranging from a few percent to 100%. The Ly alpha escape fraction in LAEs correlates with E(B - V) in a way that is expected if Ly alpha photons suffer from similar amounts of dust extinction as UV continuum photons. This result implies that a strong enhancement of the Ly alpha EW with dust, due to a clumpy multi-phase interstellar medium (ISM), is not a common process in LAEs at these redshifts. It also suggests that while in other galaxies Ly alpha can be preferentially quenched by dust due to its scattering nature, this is not the case in LAEs. We find no evolution in the average dust content and Ly alpha escape fraction of LAEs from z similar to 4 to 2. We see hints of a drop in the number density of LAEs from z similar to 4 to 2 in the redshift distribution and the Ly alpha luminosity function, although larger samples are required to confirm this. The mean Ly alpha escape fraction of the overall galaxy population decreases significantly from z similar to 6 to z similar to 2, in agreement with recent results. Our results point toward a scenario in which star-forming galaxies build up significant amounts of dust in their ISM between z similar to 6 and 2, reducing their Ly alpha escape fraction, with LAE selection preferentially detecting galaxies which have the highest escape fractions given their dust content. The fact that a large escape of Ly alpha photons is reached by z similar to 6 implies that better constraints on this quantity at higher redshifts might detect re-ionization in a way that is uncoupled from the effects of dust.Item The HETDEX Pilot Survey. V. The Physical Origin Of Ly Alpha Emitters Probed By Near-Infrared Spectroscopy(2014-08) Song, Mimi; Finkelstein, Steven L.; Gebhardt, Karl; Hill, Gary J.; Drory, Niv; Ashby, Matthew L. N.; Blanc, Guillermo A.; Bridge, Joanna; Chonis, Taylor; Ciardullo, Robin; Fabricius, Maximilian; Fazio, Giovanni G.; Gawiser, Eric; Gronwall, Caryl; Hagen, Alex; Huang, Jia-Sheng; Jogee, Shardha; Livermore, Rachael; Salmon, Brett; Schneider, Donald P.; Willner, S. P.; Zeimann, Gregory R.; Song, Mimi; Finkelstein, Steven L.; Gebhardt, Karl; Hill, Gary J.; Drory, Niv; Jogee, Shardha; Livermore, RachaelWe present the results from a Very Large Telescope/SINFONI and Keck/NIRSPEC near-infrared spectroscopic survey of 16 Ly alpha emitters (LAEs) at z = 2.1-2.5 in the COSMOS and GOODS-N fields discovered from the Hobby Eberly Telescope Dark Energy Experiment Pilot Survey. We detect rest-frame optical nebular lines (H alpha and/or [O III] lambda 5007) for 10 of the LAEs and measure physical properties, including the star formation rate (SFR), gas-phase metallicity, gas mass fraction, and Ly alpha velocity offset. We find that LAEs may lie below the mass-metallicity relation for continuum-selected star-forming galaxies at the same redshift. The LAEs all show velocity shifts of Ly alpha relative to the systemic redshift ranging between +85 and +296 km s(-1) with a mean of +180 km s(-1). This value is smaller than measured for continuum-selected star-forming galaxies at similar redshifts. The Ly alpha velocity offsets show a moderate correlation with the measured SFR (2.5 sigma), but no significant correlations are seen with the SFR surface density, specific SFR, stellar mass, or dynamical mass (less than or similar to 1.5 sigma). Exploring the role of dust, kinematics of the interstellar medium (ISM), and geometry on the escape of Ly alpha photons, we find no signature of selective quenching of resonantly scattered Ly alpha photons. However, we also find no evidence that a clumpy ISM is enhancing the Ly alpha equivalent width. Our results suggest that the low metallicity in LAEs may be responsible for yielding an environment with a low neutral hydrogen column density and less dust, easing the escape of Ly alpha photons over that in continuum-selected star-forming galaxies.Item Hydrostatic Gas Constraints On Supermassive Black Hole Masses: Implications For Hydrostatic Equilibrium And Dynamical Modeling In A Sample Of Early-Type Galaxies(2009-10) Humphrey, Phillip J.; Buote, David A.; Brighenti, Fabrizio; Gebhardt, Karl; Mathews, William G.; Gebhardt, KarlWe present new mass measurements for the supermassive black holes (SMBHs) in the centers of three early-type galaxies. The gas pressure in the surrounding, hot interstellar medium (ISM) is measured through spatially resolved spectroscopy with the Chandra X-ray Observatory, allowing the SMBH mass (M(BH)) to be inferred directly under the hydrostatic approximation. This technique does not require calibration against other SMBH measurement methods and its accuracy depends only on the ISM being close to hydrostatic, which is supported by the smooth X-ray isophotes of the galaxies. Combined with results from our recent study of the elliptical galaxy NGC4649, this brings the number of galaxies with SMBHs measured in this way to four. Of these, three already have mass determinations from the kinematics of either the stars or a central gas disk, and hence join only a handful of galaxies with MBH measured by more than one technique. We find good agreement between the different methods, providing support for the assumptions implicit in both the hydrostatic and the dynamical models. The stellar mass-to-light ratios for each galaxy inferred by our technique are in agreement with the predictions of stellar population synthesis models assuming a Kroupa initial mass function (IMF). This concurrence implies that no more than similar to 10%-20% of the ISM pressure is nonthermal, unless there is a conspiracy between the shape of the IMF and nonthermal pressure. Finally, we compute Bondi accretion rates (M(bondi)), finding that the two galaxies with the highest M(bondi) exhibit little evidence of X-ray cavities, suggesting that the correlation with the active galactic nuclei jet power takes time to be established.Item The Interstellar Medium And Feedback In The Progenitors Of The Compact Passive Galaxies At Z Similar To 2(2015-02) Williams, Christina C.; Giavalisco, Mauro; Lee, Bomee; Tundo, Elena; Mobasher, Bahram; Nayyeri, Hooshang; Ferguson, Henry C.; Koekemoer, Anton; Trump, Jonathan R.; Cassata, Paolo; Dekel, Avishai; Guo, Yicheng; Lee, Kyoung-Soo; Pentericci, Laura; Bell, Eric F.; Castellano, Marco; Finkelstein, Steven L.; Fontana, Adriano; Grazian, Andrea; Grogin, Norman; Kocevski, Dale; Koo, David C.; Lucas, Ray A.; Ravindranath, Swara; Santini, Paola; Vanzella, Eros; Weiner, Benjamin J.; Finkelstein, Steven L.Quenched galaxies at z > 2 are nearly all very compact relative to z similar to 0, suggesting a physical connection between high stellar density and efficient, rapid cessation of star-formation. We present rest-frame UV spectra of Lyman-break galaxies (LBGs) at z similar to 3 selected to be candidate progenitors of the quenched galaxies at z similar to 2 based on their compact rest-frame-optical sizes and high Sigma(SFR). We compare their UV properties to those of more extended LBGs of similar mass and star-formation rate (non-candidates). We find that candidate progenitors have faster bulk interstellar medium (ISM) gas velocities and higher equivalent widths of interstellar absorption lines, implying larger velocity spread among absorbing clouds. Candidates deviate from the relationship between equivalent widths of Ly alpha and interstellar absorption lines in that their Ly alpha emission remains strong despite high interstellar absorption, possibly indicating that the neutral H I fraction is patchy, such that Ly alpha photons can escape. We detect stronger CIV P-Cygni features (emission and absorption) and He II emission in candidates, indicative of larger populations of metal-rich Wolf-Rayet stars compared to non-candidates. The faster bulk motions, broader spread of gas velocity, and Ly alpha properties of candidates are consistent with their ISM being subject to more energetic feedback than non-candidates. Together with their larger metallicity (implying more evolved star-formation activity) this leads us to propose, if speculatively, that they are likely to quench sooner than non-candidates, supporting the validity of selection criteria used to identify them as progenitors of z similar to 2 passive galaxies. We propose that massive, compact galaxies undergo more rapid growth of their stellar mass content, perhaps because the gas accretion mechanisms are different, and quench sooner than normally sized LBGs at these (early) epochs.Item A Lack of Resolved Near-Infrared Polarization Across the Face of M51(2012-12) Pavel, Michael D.; Clemens, Dan P.; Pavel, Michael D.The galaxy M51 was observed using the Mimir instrument on the Perkins Telescope to constrain the resolved H-band (1.6 mu m) polarization across the galaxy. These observations place an upper limit of P-H < 0.05% on the H-band polarization across the face of M51, at 0.6 arcsec pixel sampling. Even with smoothing to coarser angular resolutions, to reduce polarization uncertainty, the H-band polarization remains undetected. The polarization upper limit at H band, when combined with previous resolved optical polarimetry, rules out a Serkowski-like polarization dependence on wavelength. Other polarization mechanisms cannot account for the observed polarization ratio (P-H/P-VRI less than or similar to 0.05) across the face of M51.Item The Metallicity Dependence Of The Co -> H-2 Conversion Factor In Z >= 1 Star-Forming Galaxies(2012-02) Genzel, R.; Tacconi, L. J.; Combes, Francoise; Bolatto, A.; Neri, R.; Sternberg, Assaf; Cooper, Michael C.; Bouche, N.; Bournaud, F.; Burkert, A.; Comerford, J.; Cox, P.; Davis, M.; Schreiber, N. M. F.; Garcia-Burillo, S.; Gracia-Carpio, J.; Lutz, D.; Naab, T.; Newman, S.; Saintonge, A.; Shapiro, K.; Shapley, A.; Weiner, B.; Comerford, J.We use the first systematic samples of CO millimeter emission in z >= 1 "main-sequence" star-forming galaxies to study the metallicity dependence of the conversion factor alpha(CO), from CO line luminosity to molecular gas mass. The molecular gas depletion rate inferred from the ratio of the star formation rate (SFR) to CO luminosity, is similar to 1 Gyr(-1) for near-solar metallicity galaxies with stellar masses above M-S similar to 10(11) M-circle dot. In this regime, the depletion rate does not vary more than a factor of two to three as a function of molecular gas surface density or redshift between z similar to 0 and 2. Below M-S the depletion rate increases rapidly with decreasing metallicity. We argue that this trend is not caused by starburst events, by changes in the physical parameters of the molecular clouds, or by the impact of the fundamental-metallicity-SFR-stellar mass relation. A more probable explanation is that the conversion factor is metallicity dependent and that star formation can occur in "CO-dark" gas. The trend is also expected theoretically from the effect of enhanced photodissociation of CO by ultraviolet radiation at low metallicity. From the available z similar to 0 and z similar to 1-3 samples we constrain the slope of the log(alpha CO)-log (metallicity) relation to range between -1 and -2, fairly insensitive to the assumed slope of the gas-SFR relation. Because of the lower metallicities near the peak of the galaxy formation activity at z similar to 1-2 compared to z similar to 0, we suggest that molecular gas masses estimated from CO luminosities have to be substantially corrected upward for galaxies below M-S.Item New Constraints On Dust Emission And UV Attenuation Of Z=6.5-7.5 Galaxies From Millimeter Observations(2015-02) Schaerer, D.; Boone, F.; Zamojski, M.; Staguhn, J.; Dessauges-Zavadsky, M.; Finkelstein, S.; Combes, F.; Finkelstein, S.Context. Determining the dust properties and UV attenuation of distant star-forming galaxies is of great interest for our understanding of galaxy formation and cosmic star formation in the early Universe. However, few direct measurements exist so far. Aims. To shed new light on these questions, we have targeted two recently discovered Lyman-break galaxies (LBGs) at z approximate to 6.8 and z = 7.508 to search for dust continuum and [C II] 1158 pm line emission. Methods. The strongly lensed z approximate to 6.8 LBG A1703-zD1 behind the galaxy cluster Abell 1703 and the spectroscopically confirmed z = 7.508 LBG z8-GND-5296 in the GOODS-N field were observed with the Plateau de Bure Interferometer (PdBI) at 1.2 mm. These observations were combined with those of three z > 6.5 Ly alpha emitters (HCM6A, Himiko, and IOK-1), for which deep measurements were recently obtained with the PdBI and ALMA. Results. [C II] is undetected in both galaxies, providing a deep upper limit of L-[C II] < 2.8 x 10(7) L for A1703-zD1, comparable to the nondetections of Himiko and IOK-1 with ALMA. Dust continuum emission from A1703-zD1 and z8-GND-5296 is not detected with an rms of 0.12 and 0.16 mJy/beam. From these nondetections and earlier multiwavelength observations we derive upper limits on their IR luminosity and star formation rate, dust mass, and UV attenuation. Thanks to strong gravitational lensing, the achieved limit for A1703-zDI is similar to those achieved with ALMA, probing below the luminous infrared galaxy (LIRG) regime (L-IR < 8.1 x 10(10) L-circle dot) and very low dust masses (M-d < 1.6 x 10(7) M-circle dot). We find that all five galaxies are compatible with the Calzetti IRX-beta relation, their UV attenuation is compatible with several indirect estimates from other methods (the UV slope, extrapolation of the attenuation measured from the IR/UV ratio at lower redshift, and spectral energy distribution fits), and the dust-to-stellar mass ratio is compatible with that of galaxies from z = 0 to 3. From their stellar mass, the high-z galaxies studied here have an attenuation below the one expected from the mean relation of low-redshift (z less than or similar to 1.5) galaxies. Conclusions. More and deeper (sub-)mm data are clearly needed to directly determine the UV attenuation and dust content of the dominant population of high-z star-forming galaxies and to establish their dependence on stellar mass, redshift, and other properties more firmly.Item Nuclear Star-Forming Ring of the Milky Way: Simulations(2011-07) Kim, Sungsoo S.; Saitoh, Takayuki R.; Jeon, Myouungwon; Figer, Donald F.; Merritt, David; Wada, Keiichi; Jeon, MyouungwonWe present hydrodynamic simulations of gas clouds in the central kpc region of the Milky Way that is modeled with a three-dimensional bar potential. Our simulations consider realistic gas cooling and heating, star Formation, and supernova feedback. A ring of dense gas clouds forms as a result of X-1-X-2 orbit transfer, and our potential model results in a ring radius of similar to 200 pc, which coincides with the extraordinary reservoir of dense molecular clouds in the inner bulge, the Central Molecular Zone (CMZ). The gas clouds accumulated in the CMZ can reach high enough densities to form stars, and with an appropriate choice of simulation parameters, we successfully reproduce the observed gas mass and the star Formation rate (SFR) in the CMZ, similar to 2 x 10(7) M-circle dot and similar to 0.1 M-circle dot yr(-1). Star Formation in our simulations takes place mostly in the outermost X-2 orbits, and the SFR per unit surface area outside the CMZ is much lower. These facts suggest that the inner Galactic bulge may harbor a mild version of the nuclear star-forming rings seen in some external disk galaxies. Furthermore, from the relatively small size of the Milky Way's nuclear bulge, which is thought to be a result of sustained star Formation in the CMZ, we infer that the Galactic inner bulge probably had a shallower density profile or stronger bar elongation in the past.Item On The Source Of The Dust Extinction In Type Ia Supernovae And The Discovery Of Anomalously Strong Na I Absorption(2013-12) Phillips, Mark M.; Simon, Joshua D.; Morrell, Nidia; Burns, Christopher R.; Cox, Nick L. J.; Foley, Ryan J.; Karakas, Amanda I.; Patat, F.; Sternberg, Assaf; Williams, R. E.; Gal-Yam, Avishay; Hsiao, Eric Y.; Leonard, D. C.; Persson, Sven E.; Stritzinger, Maximilian; Thompson, Ian B.; Campillay, Abdo; Contreras, Carlos; Folatelli, Gaston; Freedman, Wendy L.; Hamuy, Mario; Roth, Miguel; Shields, Gregory A.; Suntzeff, Nicholas B.; Chomiuk, Laura; Ivans, Inese I.; Madore, Barry F.; Penprase, B. E.; Perley, Daniel; Pignata, G.; Preston, G.; Soderberg, Alicia M.; Shields, Gregory A.High-dispersion observations of the Na I D lambda lambda 5890, 5896 and K I lambda lambda 7665, 7699 interstellar lines, and the diffuse interstellar band at 5780 angstrom in the spectra of 32 Type Ia supernovae are used as an independent means of probing dust extinction. We show that the dust extinction of the objects where the diffuse interstellar band at 5780 angstrom is detected is consistent with the visual extinction derived from the supernova colors. This strongly suggests that the dust producing the extinction is predominantly located in the interstellar medium of the host galaxies and not in circumstellar material associated with the progenitor system. One quarter of the supernovae display anomalously large Na I column densities in comparison to the amount of dust extinction derived from their colors. Remarkably, all of the cases of unusually strong Na I D absorption correspond to "Blueshifted" profiles in the classification scheme of Sternberg et al. This coincidence suggests that outflowing circumstellar gas is responsible for at least some of the cases of anomalously large Na I column densities. Two supernovae with unusually strong Na I D absorption showed essentially normal K I column densities for the dust extinction implied by their colors, but this does not appear to be a universal characteristic. Overall, we find the most accurate predictor of individual supernova extinction to be the equivalent width of the diffuse interstellar band at 5780 angstrom, and provide an empirical relation for its use. Finally, we identify ways of producing significant enhancements of the Na abundance of circumstellar material in both the single-degenerate and double-degenerate scenarios for the progenitor system.Item PHIBSS: Molecular Gas Content And Scaling Relations In Z Similar To 1-3 Massive, Main-Sequence Star-Forming Galaxies(2013-05) Tacconi, L. J.; Neri, R.; Genzel, R.; Combes, Francoise; Bolatto, A.; Cooper, Michael C.; Wuyts, S.; Bournaud, F.; Burkert, A.; Comerford, J.; Cox, P.; Davis, M.; Schreiber, N. M. F.; Garcia-Burillo, S.; Gracia-Carpio, J.; Lutz, D.; Naab, T.; Newman, S.; Omont, A.; Saintonge, A.; Griffin, K. S.; Shapley, A.; Sternberg, Assaf; Weiner, B.; Comerford, J.We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO 3-2 survey of the molecular gas properties in massive, main-sequence star-forming galaxies (SFGs) near the cosmic star formation peak. PHIBSS provides 52 CO detections in two redshift slices at z similar to 1.2 and 2.2, with log(M-*(M-circle dot)) >= 10.4 and log(SFR(M-circle dot/yr)) >= 1.5. Including a correction for the incomplete coverage of the M-*-SFR plane, and adopting a "Galactic" value for the CO-H-2 conversion factor, we infer average gas fractions of similar to 0.33 at z similar to 1.2 and similar to 0.47 at z similar to 2.2. Gas fractions drop with stellar mass, in agreement with cosmological simulations including strong star formation feedback. Most of the z similar to 1-3 SFGs are rotationally supported turbulent disks. The sizes of CO and UV/optical emission are comparable. The molecular-gas-star-formation relation for the z = 1-3 SFGs is near-linear, with a similar to 0.7 Gyr gas depletion timescale; changes in depletion time are only a secondary effect. Since this timescale is much less than the Hubble time in all SFGs between z similar to 0 and 2, fresh gas must be supplied with a fairly high duty cycle over several billion years. At given z and M-*, gas fractions correlate strongly with the specific star formation rate (sSFR). The variation of sSFR between z similar to 0 and 3 is mainly controlled by the fraction of baryonic mass that resides in cold gas.Item PHIBSS: Molecular Gas, Extinction, Star Formation, And Kinematics In The Z=1.5 Star-Forming Galaxy Egs13011166(2013-08) Genzel, R.; Tacconi, L. J.; Kurk, Jaron; Wuyts, S.; Combes, Francoise; Freundlich, J.; Bolatto, A.; Cooper, Michael C.; Neri, R.; Nordon, R.; Bournaud, F.; Burkert, A.; Comerford, J.; Cox, P.; Davis, M.; Schreiber, N. M. F.; Garcia-Burillo, S.; Gracia-Carpio, J.; Lutz, D.; Naab, T.; Newman, S.; Saintonge, A.; Griffin, K. S.; Shapley, A.; Sternberg, Assaf; Weiner, B.; Comerford, J.We report matched resolution imaging spectroscopy of the CO 3-2 line (with the IRAM Plateau de Bure millimeter interferometer) and of the Ha line (with LUCI at the Large Binocular Telescope) in the massive z = 1.53 main-sequence galaxy EGS 13011166, as part of the "Plateau de Bure high-z, blue-sequence survey" (PHIBSS: Tacconi et al.). We combine these data with Hubble Space Telescope V-I-J-H-band maps to derive spatially resolved distributions of stellar surface density, star formation rate, molecular gas surface density, optical extinction, and gas kinematics. The spatial distribution and kinematics of the ionized and molecular gas are remarkably similar and are well modeled by a turbulent, globally Toomre unstable, rotating disk. The stellar surface density distribution is smoother than the clumpy rest-frame UV/ optical light distribution and peaks in an obscured, star-forming massive bulge near the dynamical center. The molecular gas surface density and the effective optical screen extinction track each other and are well modeled by a "mixed" extinction model. The inferred slope of the spatially resolved molecular gas to star formation rate relation, N = d(log)Sigma(star form)/dlog Sigma(mol) (gas), depends strongly on the adopted extinction model, and can vary from 0.8 to 1.7. For the preferred mixed dust-gas model, we find N = 1.14 +/- 0.1.Item The Spatially Resolved Star Formation Law From Integral Field Spectroscopy: Virus-P Observations Of NGC 5194(2009-10) Blanc, Guillermo A.; Heiderman, Amanda; Gebhardt, Karl; Evans, Neal J.; Adams, Joshua; Blanc, Guillermo A.; Heiderman, Amanda; Gebhardt, Karl; Evans, Neal J.; Adams, JoshuaWe investigate the relation between the star formation rate (SFR) surface density (Sigma(SFR)) and the mass surface density of gas (Sigma(gas)) in NGC 5194 (a.k.a. M51a, Whirlpool Galaxy). Visible Integral field Replicable Unit Spectrograph Prototype (VIRUS-P) integral field spectroscopy of the central 4.1 x 4.1 kpc(2) of the galaxy is used to measure H alpha, H beta, [O III]lambda 5007, [N II]lambda lambda 6548,6584, and [S II]lambda lambda 6717,6731 emission line fluxes for 735 regions similar to 170 pc in diameter. We use the Balmer decrement to calculate nebular dust extinctions, and correct the observed fluxes in order to accurately measure Sigma(SFR) in each region. Archival HI 21 cm and CO maps with spatial resolution similar to that of VIRUS-P are used to measure the atomic and molecular gas surface density for each region. We present a new method for fitting the star formation law (SFL), which includes the intrinsic scatter in the relation as a free parameter, allows the inclusion of non-detections in both Sigma(gas) and Sigma(SFR), and is free of the systematics involved in performing linear regressions over incomplete data in logarithmic space. After rejecting regions whose nebular spectrum is affected by the central active galactic nucleus in NGC 5194, we use the [S II]/H alpha ratio to separate spectroscopically the contribution from the diffuse ionized gas ( DIG) in the galaxy, which has a different temperature and ionization Statefrom those of H II regions in the disk. The DIG only accounts for 11% of the total H alpha luminosity integrated over the whole central region, but on local scales it can account for up to a 100% of the H alpha emission, especially in the inter-arm regions. After removing the DIG contribution from the H alpha fluxes, we measure a slope N = 0.82 +/- 0.05, and an intrinsic scatter epsilon = 0.43 +/- 0.02 dex for the molecular gas SFL. We also measure a typical depletion timescale tau = Sigma(HI+H2)/Sigma(SFR) approximate to 2 Gyr, in good agreement with recent measurements by Bigiel et al. The atomic gas density shows no correlation with the SFR, and the total gas SFL in the sampled density range closely follows the molecular gas SFL. Integral field spectroscopy allows a much cleaner measurement of H alpha emission line fluxes than narrow-band imaging, since it is free of the systematics introduced by continuum subtraction, underlying photospheric absorption, and contamination by the [N II] doublet. We assess the validity of different corrections usually applied in narrow-band measurements to overcome these issues and find that while systematics are introduced by these corrections, they are only dominant in the low surface brightness regime. The disagreement with the previous measurement of a super-linear molecular SFL by Kennicutt et al. is most likely due to differences in the fitting method. Our results support the recent evidence for a low, and close to constant, star formation efficiency (SFE = tau(-1)) in the molecular component of the interstellar medium. The data show an excellent agreement with the recently proposed model of the SFL by Krumholz et al. The large intrinsic scatter observed may imply the existence of other parameters, beyond the availability of gas, which are important in setting the SFR.Item The Spectrally Resolved Lyman-Alpha Emission Of Three Lyman-Alpha-Selected Field Galaxies At Z Similar To 2.4 From The HETDEX Pilot Survey(2013-10) Chonis, Taylor S.; Blanc, Guillermo A.; Hill, Gary J.; Adams, Joshua J.; Finkelstein, Steven L.; Gebhardt, Karl; Kollmeier, Juna A.; Ciardullo, Robin; Drory, Niv; Gronwall, Caryl; Hagen, Alex; Overzier, Roderik A.; Song, Mimi; Zeimann, Gregory R.; Chonis, Taylor S.; Finkelstein, Steven L.; Gebhardt, Karl; Overzier, Roderik A.We present new results on the spectrally resolved Ly alpha emission of three Ly alpha-emitting field galaxies at z similar to 2.4 with high Lya equivalent width (> 100 angstrom) and Lya luminosity (similar to 10(43) erg s(-1)). At 120 km s(-1) (FWHM) spectral resolution, the prominent double-peaked Lya profile straddles the systemic velocity, where the velocity zero point is determined from spectroscopy of the galaxies' rest-frame optical nebular emission lines. The average velocity offset from systemic of the stronger redshifted emission component for our sample is 176 km s(-1) while the average total separation between the redshifted and main blueshifted emission components is 380 km s(-1). These measurements are a factor of similar to 2 smaller than for UV-continuum-selected galaxies that show Lya in emission with lower Lya equivalent widths. We compare our Lya spectra to the predicted line profiles of a spherical "expanding shell" Ly alpha radiative transfer grid that models large-scale galaxy outflows. Specifically, blueward of the systemic velocity where two galaxies show a weak, highly blueshifted (by similar to 1000 km s(-1)) tertiary emission peak, the model line profiles are a relatively poor representation of the observed spectra. Since the neutral gas column density has a dominant influence over the shape of the Lya line profile, we caution against equating the observed Lya velocity offset with a physical outflow velocity, especially at lower spectral resolution where the unresolved Lya velocity offset is a convoluted function of several degenerate parameters. Referring to rest-frame ultraviolet and optical Hubble Space Telescope imaging, we find that galaxy-galaxy interactions may play an important role in inducing a starburst that results in copious Lya emission as well as perturbing the gas distribution and velocity field, both of which have strong influence over the Lya emission line profile.