Browsing by Subject "molecular gas"

Now showing 1 - 8 of 8

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. Mentuch
Data 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.
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 Mentuch
In 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.
Frequency And Properties Of Bars In Cluster And Field Galaxies At Intermediate Redshifts
(2009-04) Barazza, F. D.; Jablonka, P.; Desai, V.; Jogee, S.; Aragon-Salamanca, A.; De Lucia, G.; Saglia, R. P.; Halliday, C.; Poggianti, B. M.; Dalcanton, J. J.; Rudnick, G.; Milvang-Jensen, B.; Noll, S.; Simard, L.; Clowe, D. I.; Pello, R.; White, S. D. M.; Zaritsky, D.; Jogee, S.
We present a study of large-scale bars in field and cluster environments out to redshifts of similar to 0.8 using a final sample of 945 moderately inclined disk galaxies drawn from the EDisCS project. We characterize bars and their host galaxies and look for relations between the presence of a bar and the properties of the underlying disk. We investigate whether the fraction and properties of bars in clusters are different from their counterparts in the field. The properties of bars and disks are determined by ellipse fits to the surface brightness distribution of the galaxies using HST/ACS images in the F814W filter. The bar identification is based on quantitative criteria after highly inclined (> 60 degrees) systems have been excluded. The total optical bar fraction in the redshift range z = 0.4-0.8 (median z = 0.60), averaged over the entire sample, is 25% (20% for strong bars). For the cluster and field subsamples, we measure bar fractions of 24% and 29%, respectively. We find that bars in clusters are on average longer than in the field and preferentially found close to the cluster center, where the bar fraction is somewhat higher (similar to 31%) than at larger distances (similar to 18%). These findings however rely on a relatively small subsample and might be affected by small number statistics. In agreement with local studies, we find that disk-dominated galaxies have a higher optical bar fraction (similar to 45%) than bulge-dominated galaxies (similar to 15%). This result is based on Hubble types and effective radii and does not change with redshift. The latter finding implies that bar formation or dissolution is strongly connected to the emergence of the morphological structure of a disk and is typically accompanied by a transition in the Hubble type. The question whether internal or external factors are more important for bar formation and evolution cannot be answered definitely. On the one hand, the bar fraction and properties of cluster and field samples of disk galaxies are quite similar, indicating that internal processes are crucial for bar formation. On the other hand, we find evidence that cluster centers are favorable locations for bars, which suggests that the internal processes responsible for bar growth are supported by the typical interactions taking place in such environments.
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).
High-Resolution Spectroscopy Of Ne II Emission From AA Tau And GM Aur
(2009-05) Najita, Joan R.; Doppmann, Greg W.; Bitner, Martin A.; Richter, Matthew J.; Lacy, John H.; Jaffe, Daniel T.; Carr, John S.; Meijerink, Rowin; Blake, Geoffrey A.; Herczeg, Gregory J.; Glassgold, Alfred E.; Jaffe, Daniel T.
We present high-resolution (R = 80,000) spectroscopy of [Ne II] emission from two young stars, GM Aur and AA Tau, which have moderate to high inclinations. The emission from both sources appears centered near the stellar velocity and is broader than the [Ne II] emission measured previously for the face-on disk system TW Hya. These properties are consistent with a disk origin for the [Ne II] emission we detect, with disk rotation (rather than photoevaporation or turbulence in a hot disk atmosphere) playing the dominant role in the origin of the line width. In the non-face-on systems, the [Ne II] emission is narrower than the CO fundamental emission from the same sources. If the widths of both diagnostics are dominated by Keplerian rotation, this suggests that the [Ne II] emission arises from larger disk radii on average than does the CO emission. The equivalent width of the [Ne II] emission we detect is less than that of the spectrally unresolved [Ne II] feature in the Spitzer spectra of the same sources. Variability in the [Ne II] emission or the mid-infrared continuum, a spatially extended [Ne II] component, or a very (spectrally) broad [Ne II] component might account for the difference in the equivalent widths.
Keck-I Mosfire Spectroscopy Of Compact Star-Forming Galaxies At Z Greater Than Or Similar To 2: High Velocity Dispersions In Progenitors Of Compact Quiescent Galaxies
(2014-11) Barro, Guillermo; Trump, Jonathan R.; Koo, David C.; Dekel, Avishai; Kassin, Susan A.; Kocevski, Dale D.; Faber, Sandra M.; van der Wel, Arjen; Guo, Yicheng; Perez-Gonzalez, Pablo G.; Toloba, Elisa; Fang, Jerome J.; Pacifici, Camilla; Simons, Raymond; Campbell, Randy D.; Ceverino, Daniel; Finkelstein, Steven L.; Goodrich, Bob; Kassis, Marc; Koekemoer, Anton M.; Konidaris, Nicholas P.; Livermore, Rachael C.; Lyke, James E.; Mobasher, Bahram; Nayyeri, Hooshang; Peth, Michael; Primack, Joel R.; Rizzi, Luca; Somerville, Rachel S.; Wirth, Gregory D.; Zolotov, Adi; Finkelstein, Steven L.; Livermore, Rachael C.
We present Keck-I MOSFIRE near-infrared spectroscopy for a sample of 13 compact star-forming galaxies (SFGs) at redshift 2 <= z <= 2.5 with star formation rates of SFR similar to 100M(circle dot)yr(-1) and masses of log( M/M-circle dot) similar to 10.8. Their high integrated gas velocity dispersions of sigma(int) = 230(-30)(+40)km s(-1), as measured from emission lines of Ha and [O III], and the resultant M-star-sigma(int) relation and M-star-M-dyn all match well to those of compact quiescent galaxies at z similar to 2, as measured from stellar absorption lines. Since log( M-star/M-dyn)= -0.06 +/- 0.2 dex, these compact SFGs appear to be dynamically relaxed and evolved, i.e., depleted in gas and dark matter (<13(-13)(+17)%), and present larger sint than their non-compact SFG counterparts at the same epoch. Without infusion of external gas, depletion timescales are short, less than similar to 300 Myr. This discovery adds another link to our new dynamical chain of evidence that compact SFGs at z greater than or similar to 2 are already losing gas to become the immediate progenitors of compact quiescent galaxies by z similar to 2.
Millimeter Observations Of A Sample Of High-Redshift Obscured Quasars
(2009-11) Martinez-Sansigre, Alejo; Karim, Alexander; Schinnerer, Eva; Omont, Alain; Smith, Daniel J. B.; Wu, Jingwen; Hill, Gary J.; Klockner, Hans-rainer; Lacy, Mark; Rawlings, Steve; Willott, Chris J.; Hill, Gary J.
We present observations at 1.2 mm with Max-Planck Millimetre Bolometer Array (MAMBO-II) of a sample of z greater than or similar to 2 radio-intermediate obscured quasars, as well as CO observations of two sources with the Plateau de Bure Interferometer. The typical rms noise achieved by the MAMBO observations is 0.55 mJy beam(-1) and five out of 21 sources (24%) are detected at a significance of >= 3 sigma. Stacking all sources leads to a statistical detection of < S(1.2 mm)> = 0.96 +/- 0.11 mJy and stacking only the non-detections also yields a statistical detection, with < S(1.2 mm)> = 0.51 +/- 0.13 mJy. At the typical redshift of the sample, z = 2, 1 mJy corresponds to a far-infrared luminosity L(FIR) similar to 4 x 10(12) L(circle dot). If the far-infrared luminosity is powered entirely by star formation, and not by active galactic nucleus heated dust, then the characteristic inferred star formation rate is similar to 700 M(circle dot) yr(-1). This far-infrared luminosity implies a dust mass of M(d) similar to 3 x 10(8) M(circle dot), which is expected to be distributed on similar to kpc scales. We estimate that such large dust masses on kpc scales can plausibly cause the obscuration of the quasars. Combining our observations at 1.2 mm with mid-and far-infrared data, and additional observations for two objects at 350 mu m using SHARC-II, we present dust spectral energy distributions (SEDs) for our sample and derive a mean SED for our sample. This mean SED is not well fitted by clumpy torus models, unless additional extinction and far-infrared re-emission due to cool dust are included. This additional extinction can be consistently achieved by the mass of cool dust responsible for the far-infrared emission, provided the bulk of the dust is within a radius similar to 2-3 kpc. Comparison of our sample to other samples of z similar to 2 quasars suggests that obscured quasars have, on average, higher far-infrared luminosities than unobscured quasars. There is a hint that the host galaxies of obscured quasars must have higher cool-dustmasses and are therefore often found at an earlier evolutionary phase than those of unobscured quasars. For one source at z = 2.767, we detect the CO(3-2) transition, with S(CO)Delta nu = 630 +/- 50 mJy km s(-1), corresponding to L(CO(3-2)) = 3.2 x 10(7) L(circle dot), or a brightness-temperature luminosity of L'(CO(3-2)) = 2.4 x 10(10) K km s(-1) pc(2). For another source at z = 4.17, the lack of detection of the CO(4-3) line suggests the line to have a brightness-temperature luminosity L'(CO(4-3)) < 1 x 10(10) K km s(-1) pc(2). Under the assumption that in these objects the high-J transitions are thermalized, we can estimate the molecular gas contents to be M(II2) = 1.9 x 10(10) M(circle dot) and < 8 x 10(9) M(circle dot), respectively. The estimated gas depletion timescales are tau(g) = 4 Myr and <16 Myr, and low gas-to-dust mass ratios of M(g)/M(d) = 19 and <20 are inferred. These values are at the low end but consistent with those of other high-redshift galaxies.
Spatially Resolved Stellar, Dust, And Gas Properties Of The Post-Interacting Whirlpool Galaxy System
(2012-08) Cooper, Erin M.; Wilson, Christine D.; Foyle, Kelly; Bendo, George; Koda, Jin; Baes, Maarten; Boquien, Mederic; Boselli, Alessandro; Ciesla, Laure; Cooray, Asantha; Eales, Steve; Galametz, Maud; Lebouteiller, Vianney; Parkin, Tara; Roussel, Helene; Sauvage, Marc; Spinoglio, Luigi; Smith, Mathew W. L.; Cooper, Erin M.
Using infrared imaging from the Herschel Space Observatory, observed as part of the Very Nearby Galaxies Survey, we investigate the spatially resolved dust properties of the interacting Whirlpool galaxy system (NGC 5194 and NGC 5195), on physical scales of similar to 1 kpc. Spectral energy distribution modeling of the new infrared images in combination with archival optical and near-through mid-infrared images confirms that both galaxies underwent a burst of star formation similar to 370-480 Myr ago and provides spatially resolved maps of the stellar and dust mass surface densities. The resulting average dust-to-stellar mass ratios are comparable to other spiral and spheroidal galaxies studied with Herschel, with NGC 5194 at log(M-dust/M-star) = -2.5 +/- 0.2 and NGC 5195 at log(M-dust/M-star) = -3.5 +/- 0.3. The dust-to-stellar mass ratio is constant across NGC 5194 suggesting the stellar and dust components are coupled. In contrast, the mass ratio increases with radius in NGC 5195 with decreasing stellar mass density. Archival mass surface density maps of the neutral and molecular hydrogen gas are also folded into our analysis, revealing a fairly constant gas-to-dust mass ratio, 94 +/- 17 across the system. Somewhat surprisingly, we find the dust in NGC 5195 is heated by a strong interstellar radiation field (ISRF), over 20 times that of the ISRF in the Milky Way, resulting in relatively high characteristic dust temperatures (similar to 30 K). This post-starburst galaxy contains a substantial amount of low-density molecular gas and displays a gas-to-dust ratio (73 +/- 35) similar to spiral galaxies. It is unclear why the dust in NGC 5195 is heated to such high temperatures as there is no star formation in the galaxy and its active galactic nucleus is 5-10 times less luminous than the one in NGC 5194, which exhibits only a modest enhancement in the amplitude of its ISRF.