376 research outputs found
Dark and Baryonic Matter in Bright Spiral Galaxies: I.Near-infrared and Optical Broadband Surface Photometry of 30 Galaxies
We present photometrically calibrated images and surface photometry in the B,
V, R, J, H, and K-bands of 25, and in the g, r, and K-bands of 5 nearby bright
(Bo_T<12.5 mag) spiral galaxies with inclinations between 30-65 degrees
spanning the Hubble Sequence from Sa to Scd. Data are from The Ohio State
University Bright Spiral Galaxy Survey, the Two Micron All Sky Survey, and the
Sloan Digital Sky Survey Second Data Release. Radial surface brightness
profiles are extracted, and integrated magnitudes are measured from the
profiles. Axis ratios, position angles, and scale lengths are measured from the
near-infrared images. A 1-dimensional bulge/disk decomposition is performed on
the near-infrared images of galaxies with a non-negligible bulge component, and
an exponential disk is fit to the radial surface brightness profiles of the
remaining galaxies.Comment: 28 page
Geometry of Star-Forming Galaxies from SDSS, 3D-HST and CANDELS
We determine the intrinsic, 3-dimensional shape distribution of star-forming
galaxies at 0<z<2.5, as inferred from their observed projected axis ratios. In
the present-day universe star-forming galaxies of all masses 1e9 - 1e11 Msol
are predominantly thin, nearly oblate disks, in line with previous studies. We
now extend this to higher redshifts, and find that among massive galaxies (M* >
1e10 Msol) disks are the most common geometric shape at all z < 2. Lower-mass
galaxies at z>1 possess a broad range of geometric shapes: the fraction of
elongated (prolate) galaxies increases toward higher redshifts and lower
masses. Galaxies with stellar mass 1e9 Msol (1e10 Msol) are a mix of roughly
equal numbers of elongated and disk galaxies at z~1 (z~2). This suggests that
galaxies in this mass range do not yet have disks that are sustained over many
orbital periods, implying that galaxies with present-day stellar mass
comparable to that of the Milky Way typically first formed such sustained
stellar disks at redshift z~1.5-2. Combined with constraints on the evolution
of the star formation rate density and the distribution of star formation over
galaxies with different masses, our findings imply that, averaged over cosmic
time, the majority of stars formed in disks.Comment: Published in ApJ Letter
On the Evolution of the Velocity-Mass-Size Relations of Disk-Dominated Galaxies over the Past 10 Billion Years
We study the evolution of the scaling relations between maximum circular
velocity, stellar mass and optical half-light radius of star-forming
disk-dominated galaxies in the context of LCDM-based galaxy formation models.
Using data from the literature combined with new data from the DEEP2 and AEGIS
surveys we show that there is a consistent observational and theoretical
picture for the evolution of these scaling relations from z\sim 2 to z=0. The
evolution of the observed stellar scaling relations is weaker than that of the
virial scaling relations of dark matter haloes, which can be reproduced, both
qualitatively and quantitatively, with a simple, cosmologically-motivated model
for disk evolution inside growing NFW dark matter haloes. In this model optical
half-light radii are smaller, both at fixed stellar mass and maximum circular
velocity, at higher redshifts. This model also predicts that the scaling
relations between baryonic quantities evolve even more weakly than the
corresponding stellar relations. We emphasize, though, that this weak evolution
does not imply that individual galaxies evolve weakly. On the contrary,
individual galaxies grow strongly in mass, size and velocity, but in such a way
that they move largely along the scaling relations. Finally, recent
observations have claimed surprisingly large sizes for a number of star-forming
disk galaxies at z \sim 2, which has caused some authors to suggest that high
redshift disk galaxies have abnormally high spin parameters. However, we argue
that the disk scale lengths in question have been systematically overestimated
by a factor \sim 2, and that there is an offset of a factor \sim 1.4 between
H\alpha sizes and optical sizes. Taking these effects into account, there is no
indication that star forming galaxies at high redshifts (z\sim 2) have
abnormally high spin parameters.Comment: 19 pages, 10 figures, accepted to MNRAS, minor changes to previous
versio
Star Formation in AEGIS Field Galaxies since z=1.1 : The Dominance of Gradually Declining Star Formation, and the Main Sequence of Star-Forming Galaxies
We analyze star formation (SF) as a function of stellar mass (M*) and
redshift z in the All Wavelength Extended Groth Strip International Survey
(AEGIS). For 2905 field galaxies, complete to 10^10(10^10.8) Msun at z<0.7(1),
with Keck spectroscopic redshifts out to z=1.1, we compile SF rates (SFR) from
emission lines, GALEX, and Spitzer MIPS 24 micron photometry, optical-NIR M*
measurements, and HST morphologies. Galaxies with reliable signs of SF form a
distinct "main sequence (MS)", with a limited range of SFR at a given M* and z
(1 sigma < +-0.3 dex), and log(SFR) approximately proportional to log(M*). The
range of log(SFR) remains constant to z>1, while the MS as a whole moves to
higher SFR as z increases. The range of SFR along the MS constrains the
amplitude of episodic variations of SF, and the effect of mergers on SFR.
Typical galaxies spend ~67(95)% of their lifetime since z=1 within a factor of
<~ 2(4) of their average SFR at a given M* and z. The dominant mode of the
evolution of SF since z~1 is apparently a gradual decline of the average SFR in
most individual galaxies, not a decreasing frequency of starburst episodes, or
a decreasing factor by which SFR are enhanced in starbursts. LIRGs at z~1 seem
to mostly reflect the high SFR typical for massive galaxies at that epoch. The
smooth MS may reflect that the same set of few physical processes governs star
formation prior to additional quenching processes. A gradual process like gas
exhaustion may play a dominant role.Comment: 5 pages, 1 figure, emulateapj; ApJ Letters, accepted; AEGIS special
issue; proof-level corrections added; title change
Keck-I MOSFIRE spectroscopy of compact star-forming galaxies at z2: High velocity dispersions in progenitors of compact quiescent galaxies
We present Keck-I MOSFIRE near-infrared spectroscopy for a sample of 13
compact star-forming galaxies (SFGs) at redshift with star
formation rates of SFR100M y and masses of
log(M/M). Their high integrated gas velocity dispersions of
=230 km s, as measured from emission
lines of H and [OIII], and the resultant
M relation and MM all
match well to those of compact quiescent galaxies at , as measured from
stellar absorption lines. Since log(M/M)
dex, these compact SFGs appear to be dynamically relaxed and more evolved,
i.e., more depleted in gas and dark matter (13\%) than their
non-compact SFG counterparts at the same epoch. Without infusion of external
gas, depletion timescales are short, less than 300 Myr. This discovery
adds another link to our new dynamical chain of evidence that compact SFGs at
are already losing gas to become the immediate progenitors of
compact quiescent galaxies by .Comment: 12 pages, 7 figures, submitted to Ap
Galaxy Luminosity Functions to z~1: DEEP2 vs. COMBO-17 and Implications for Red Galaxy Formation
The DEEP2 and COMBO-17 surveys are used to study the evolution of the
luminosity function of red and blue galaxies to . Schechter function
fits show that, since , dims by 1.3 mag per unit redshift
for both color classes, of blue galaxies shows little change, while
for red galaxies has formally nearly quadrupled. At face value, the
number density of blue galaxies has remained roughly constant since ,
whereas that of red galaxies has been rising. Luminosity densities support both
conclusions, but we note that most red-galaxy evolution occurs between our data
and local surveys and in our highest redshift bin, where the data are weakest.
We discuss the implications of having most red galaxies emerge after
from precursors among the blue population, taking into account the properties
of local and distant E/S0s. We suggest a ``mixed'' scenario in which some blue
galaxies have their star-formation quenched in gas-rich mergers, migrate to the
red sequence with a variety of masses, and merge further on the red sequence in
one or more purely stellar mergers. E/S0s of a given mass today will have
formed via different routes, in a manner that may help to explain the
fundamental plane and other local scaling laws.Comment: Submitted to ApJ. 73 pages, 12 figures. Part II of a two-paper
series. The entire paper is available as a single postscript file at:
http://www.ucolick.org/~cnaw/paper2_submitted.ps.g
The inferred evolution of the cold gas properties of CANDELS galaxies at 0.5 <z <3.0
We derive the total cold gas, atomic hydrogen, and molecular gas masses of
approximately 24 000 galaxies covering four decades in stellar mass at
redshifts 0.5 < z < 3.0, taken from the CANDELS survey. Our inferences are
based on the inversion of a molecular hydrogen based star formation law,
coupled with a prescription to separate atomic and molecular gas. We find that:
1) there is an increasing trend between the inferred cold gas (HI and H2), HI,
and H2 mass and the stellar mass of galaxies down to stellar masses of 10^8
Msun already in place at z = 3; 2) the molecular fractions of cold gas increase
with increasing stellar mass and look-back time; 3) there is hardly any
evolution in the mean HI content of galaxies at fixed stellar mass; 4) the cold
gas fraction and relative amount of molecular hydrogen in galaxies decrease at
a relatively constant rate with time, independent of stellar mass; 5) there is
a large population of low-stellar mass galaxies dominated by atomic gas. These
galaxies are very gas rich, but only a minor fraction of their gas is
molecular; 6) the ratio between star-formation rate (SFR) and inferred total
cold gas mass (HI + H2) of galaxies (i.e., star-formation efficiency; SFE)
increases with star-formation at fixed stellar masses. Due to its simplicity,
the presented approach is valuable to assess the impact of selection biases on
small samples of directly-observed gas masses and to extend scaling relations
down to stellar mass ranges and redshifts that are currently difficult to probe
with direct measurements of gas content.Comment: Accepted for publication in MNRAS. 22 pages, 18 figures. Data
products are available at
http://www.eso.org/~gpopping/Gergo_Poppings_Homepage/Data.htm
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