Browsing by Subject "disk"

Now showing 1 - 9 of 9

Accretion Onto Planetary Mass Companions of Low-Mass Young Stars
(2014-03) Zhou, Yifan; Herczeg, Gregory J.; Kraus, Adam L.; Metchev, Stanimir; Cruz, Kelle L.; Kraus, Adam L.
Measurements of accretion rates onto planetary mass objects may distinguish between different planet Formation mechanisms, which predict different accretion histories. In this Letter, we use Hubble Space Telescope (HST)/WFC3 UVIS optical photometry to measure accretion rates onto three accreting objects, GSC 06214-00210 b, GQ Lup b, and DH Tau b, that are at the planet/brown dwarf boundary and are companions to solar mass stars. The excess optical emission in the excess accretion continuum yields mass accretion rates of 10(-9)-10(-11) M-circle dot yr(-1) for these three objects. Their accretion rates are an order of magnitude higher than expected from the correlation between mass and accretion rates measured from the UV excess, which is applicable if these wide planetary mass companions formed by protostellar core fragmentation. The high accretion rates and large separation from the central star demonstrate the presence of massive disks around these objects. Models for the Formation and evolution of wide planetary mass companions should account for their large accretion rates. High ratios of Ha luminosity over accretion luminosity for objects with low accretion rates suggest that searches for Ha emission may be an efficient way to find accreting planets.
The Cluster Of Blue Stars Surrounding The M31 Nuclear Black Hole
(2012-02) Lauer, Tod R.; Bender, Ralf; Kormendy, John; Rosenfield, Philip; Green, Richard F.; Kormendy, John
We obtained U330- and B-band images of the M31 nucleus using the High Resolution Camera of the Advanced Camera for Surveys on board the Hubble Space Telescope (HST). The spatial resolution in the U-330 band, 0.'' 03 FWHM, or 0.1 pc at M31, is sufficient to resolve the outskirts of the compact cluster (P3) of UV-bright stars surrounding the M31 black hole. The center of the cluster is marked by an extended source that is both brighter and redder than the other point sources within P3; it is likely to be a blend of several bright stars. We hypothesize that it marks the location of the M31 black hole. Both stellar photometry and a surface brightness fluctuation analysis show that the P3 stellar population is consistent with early-type main-sequence stars formed in a similar to 100-200 Myr old starburst population. Evolutionary tracks of post early asymptotic giant branch (PEAGB) stars, associated with late-stage evolution of an old population, also traverse the U and U - B domain occupied by the P3 stars; but we argue that only a few stars could be accounted for that way. PEAGB evolution is very rapid, and there is no progenitor population of red giants associated with P3. The result that P3 comprises young stars is consistent with inferences from earlier HST observations of the integrated light of the cluster. Like the Milky Way, M31 harbors a black hole closely surrounded by apparently young stars.
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.
Herschel Extreme Lensing Line Observations: Dynamics Of Two Strongly Lensed Star-Forming Galaxies Near Redshift Z=2
(2014-05) Rhoads, James E.; Malhotra, Sangeeta; Allam, Sahar; Carilli, Chris; Combes, Francoise; Finkelstein, Keely; Finkelstein, Steven L.; Frye, Brenda; Gerin, Maryvonne; Guillard, Pierre; Nesvadba, Nicole; Rigby, Jane; Spaans, Marco; Strauss, Michael A.; Finkelstein, Keely; Finkelstein, Steven L.
We report on two regularly rotating galaxies at redshift z approximate to 2, using high-resolution spectra of the bright [C II] 158 mu m emission line from the HIFI instrument on the Herschel Space Observatory. Both SDSS090122.37+181432.3 ("S0901") and SDSSJ120602.09+514229.5 ("the Clone") are strongly lensed and show the double-horned line profile that is typical of rotating gas disks. Using a parametric disk model to fit the emission line profiles, we find that S0901 has a rotation speed of nu sin(i) approximate to 120 +/- 7 kms(-1) and a gas velocity dispersion of sigma(g) < 23 km s-1 (1 sigma). The best-fitting model for the Clone is a rotationally supported disk having nu sin(i) approximate to 79 +/- 11 km s(-1) and sigma(g) less than or similar to 4 kms-1 (1 sigma). However, the Clone is also consistent with a family of dispersion-dominated models having sigma(g) = 92 +/- 20 km s (1). Our results showcase the potential of the [C II] line as a kinematic probe of high-redshift galaxy dynamics: [C II] is bright, accessible to heterodyne receivers with exquisite velocity resolution, and traces dense star-forming interstellar gas. Future [C II] line observations with ALMA would offer the further advantage of spatial resolution, allowing a clearer separation between rotation and velocity dispersion.
Ionized Gas In The Galactic Center: New Observations And Interpretation
(2012-08) Irons, Wesley T.; Lacy, John H.; Richter, Matthew J.; Irons, Wesley T.; Lacy, John H.
We present new observations of the [Ne II] emission from the ionized gas in Sgr A West with improved resolution and sensitivity. About half of the emission comes from gas with kinematics indicating it is orbiting in a plane tipped about 25 degrees from the Galactic plane. This plane is consistent with that derived previously for the circumnuclear molecular disk and the northern arm and western arc ionized features. However, unlike most previous studies, we conclude that the ionized gas is not moving along the ionized features, but on more nearly circular paths. The observed speeds are close to, but probably somewhat less than expected for orbital motions in the potential of the central black hole and stars and have a small inward component. The spatial distribution of the emission is well fitted by a spiral pattern. We discuss possible physical explanations for the spatial distribution and kinematics of the ionized gas, and conclude that both may be best explained by a one-armed spiral density wave, which also accounts for both the observed low velocities and the inward velocity component. We suggest that a density wave may result from the precession of elliptical orbits in the potential of the black hole and stellar mass distribution.
The Open Cluster Chemical Analysis and Mapping Survey: Local Galactic Metallicity Gradient with APOGEE Using SDSS DR10
(2013-11) Frinchaboy, Peter M.; Thompson, Benjamin; Jackson, Kelly M.; O'Connell, Julia; Meyer, Brianne; Zasowski, Gail; Majewski, Steven R.; Chojnowksi, S. Drew; Johnson, Jennifer A.; Allende Prieto, Carlos; Beers, Timothy C.; Bizyaev, Dmitry; Brewington, Howard; Cunha, Katia; Ebelke, Garrett; Perez, Ana; Elia Garcia; Hearty, Frederick R.; Holtzman, Jon; Kinemuchi, Karen; Malanushenko, Elena; Malanushenko, Viktor; Marchante, Moses; Meszaros, Szabolcs; Muna, Demitri; Nidever, David L.; Oravetz, Daniel; Pan, Kaike; Schiavon, Ricardo P.; Schneider, Donald P.; Shetrone, Matthew; Simmons, Audrey; Snedden, Stephanie; Smith, Verne V.; Wilson, John C.; Shetrone, Matthew
The Open Cluster Chemical Analysis and Mapping (OCCAM) survey aims to produce a comprehensive, uniform, infrared-based data set for hundreds of open clusters, and constrain key Galactic dynamical and chemical parameters from this sample. This first contribution from the OCCAM survey presents analysis of 141 members stars in 28 open clusters with high-resolution metallicities derived from a large uniform sample collected as part of the Sloan Digital Sky Survey III/Apache Point Observatory Galactic Evolution Experiment. This sample includes the first high-resolution metallicity measurements for 22 open clusters. With this largest ever uniformly observed sample of open cluster stars we investigate the Galactic disk gradients of both [M/H] and [alpha/M]. We find basically no gradient in [alpha/M] across 7.9 kpc <= R-GC <= 14.5 kpc, but [M/H] does show a gradient for R-GC < 10 kpc and a significant flattening beyond R-GC = 10 kpc. In particular, whereas fitting a single linear trend yields an [M/H] gradient of -0.09 +/- 0.03 dex kpc(-1)-similar to previously measure gradients inside 13 kpc-by independently fitting inside and outside 10 kpc separately we find a significantly steeper gradient near the Sun (7.9 <= R-GC <= 10) than previously found (-0.20 +/- 0.08 dex kpc(-1)) and a nearly flat trend beyond 10 kpc (-0.02 +/- 0.09 dex kpc(-1)).
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, Joshua
We 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.
Stellar Tidal Streams In Spiral Galaxies Of The Local Volume: A Pilot Survey With Modest Aperture Telescopes
(2010-10) Martinez-Delgado, David; Gabany, R. Jay; Crawford, Ken; Zibetti, Stefano; Majewski, Steven R.; Rix, Hans-Walter; Fliri, Jurgen; Carballo-Bello, Julio A.; Bardalez-Gagliuffi, Daniella C.; Penarrubia, Jorge; Chonis, Taylor S.; Madore, Barry; Trujillo, Ignacio; Schirmer, Mischa; McDavid, David A.; Chonis, T. S.
Within the hierarchical framework for galaxy formation, minor merging and tidal interactions are expected to shape all large galaxies to the present day. As a consequence, most seemingly normal disk galaxies should be surrounded by spatially extended stellar >tidal features> of low surface brightness. As part of a pilot survey for such interaction signatures, we have carried out ultra deep, wide field imaging of eight isolated spiral galaxies in the Local Volume, with data taken at small (D = 0.1-0.5 m) robotic telescopes that provide exquisite surface brightness sensitivity (mu(lim)(V) similar to 28.5 mag arcsec(-2)). This initial observational effort has led to the discovery of six previously undetected extensive (to similar to 30 kpc) stellar structures in the halos surrounding these galaxies, likely debris from tidally disrupted satellites. In addition, we confirm and clarify several enormous stellar over-densities previously reported in the literature, but never before interpreted as tidal streams. Even this pilot sample of galaxies exhibits strikingly diverse morphological characteristics of these extended stellar features: great circle-like features that resemble the Sagittarius stream surrounding the Milky Way, remote shells and giant clouds of presumed tidal debris far beyond the main stellar body, as well as jet-like features emerging from galactic disks. Together with presumed remains of already disrupted companions, our observations also capture surviving satellites caught in the act of tidal disruption. A qualitative comparison with available simulations set in a Lambda Cold Dark Matter cosmology (that model the stellar halo as the result of satellite disruption evolution) shows that the extraordinary variety of stellar morphologies detected in this pilot survey matches that seen in those simulations. The common existence of these tidal features around >normal> disk galaxies and the morphological match to the simulations constitutes new evidence that these theoretical models also apply to a large number of other Milky Way-mass disk galaxies in the Local Volume.
Stellar Tidal Streams In Spiral Galaxies Of The Local Volume: A Pilot Survey With Modest Aperture Telescopes
(2010-10) Martinez-Delgado, David; Gabany, R. Jay; Crawford, Ken; Zibetti, Stefano; Majewski, Steven R.; Rix, Hans-Walter; Fliri, Jurgen; Carballo-Bello, Julio A.; Bardalez-Gagliuffi, Daniella C.; Penarrubia, Jorge; Chonis, Taylor S.; Madore, Barry; Trujillo, Ignacio; Schirmer, Mischa; McDavid, David A.; Chonis, T. S.
Within the hierarchical framework for galaxy formation, minor merging and tidal interactions are expected to shape all large galaxies to the present day. As a consequence, most seemingly normal disk galaxies should be surrounded by spatially extended stellar >tidal features> of low surface brightness. As part of a pilot survey for such interaction signatures, we have carried out ultra deep, wide field imaging of eight isolated spiral galaxies in the Local Volume, with data taken at small (D = 0.1-0.5 m) robotic telescopes that provide exquisite surface brightness sensitivity (mu(lim)(V) similar to 28.5 mag arcsec(-2)). This initial observational effort has led to the discovery of six previously undetected extensive (to similar to 30 kpc) stellar structures in the halos surrounding these galaxies, likely debris from tidally disrupted satellites. In addition, we confirm and clarify several enormous stellar over-densities previously reported in the literature, but never before interpreted as tidal streams. Even this pilot sample of galaxies exhibits strikingly diverse morphological characteristics of these extended stellar features: great circle-like features that resemble the Sagittarius stream surrounding the Milky Way, remote shells and giant clouds of presumed tidal debris far beyond the main stellar body, as well as jet-like features emerging from galactic disks. Together with presumed remains of already disrupted companions, our observations also capture surviving satellites caught in the act of tidal disruption. A qualitative comparison with available simulations set in a Lambda Cold Dark Matter cosmology (that model the stellar halo as the result of satellite disruption evolution) shows that the extraordinary variety of stellar morphologies detected in this pilot survey matches that seen in those simulations. The common existence of these tidal features around >normal> disk galaxies and the morphological match to the simulations constitutes new evidence that these theoretical models also apply to a large number of other Milky Way-mass disk galaxies in the Local Volume.