142 research outputs found
z~2: An Epoch of Disk Assembly
We explore the evolution of the internal gas kinematics of star-forming
galaxies from the peak of cosmic star-formation at to today.
Measurements of galaxy rotation velocity , which quantify ordered
motions, and gas velocity dispersion , which quantify disordered
motions, are adopted from the DEEP2 and SIGMA surveys. This sample covers a
continuous baseline in redshift from to , spanning 10 Gyrs. At
low redshift, nearly all sufficiently massive star-forming galaxies are
rotationally supported (). By , the percentage of
galaxies with rotational support has declined to 50 at low stellar mass
() and 70 at high stellar mass
(). For , the percentage
drops below 35 for all masses. From to now, galaxies exhibit
remarkably smooth kinematic evolution on average. All galaxies tend towards
rotational support with time, and it is reached earlier in higher mass systems.
This is mostly due to an average decline in by a factor of 3 since a
redshift of 2, which is independent of mass. Over the same time period,
increases by a factor of 1.5 for low mass systems, but does not
evolve for high mass systems. These trends in and with
time are at a fixed stellar mass and should not be interpreted as evolutionary
tracks for galaxy populations. When galaxy populations are linked in time with
abundance matching, not only does decline with time as before, but
strongly increases with time for all galaxy masses. This enhances the
evolution in . These results indicate that is a
period of disk assembly, during which the strong rotational support present in
today's massive disk galaxies is only just beginning to emerge.Comment: 12 pages, 8 figures, submitted to Ap
The relationship between galaxy and dark matter halo size from z ∼ 3 to the present
We explore empirical constraints on the statistical relationship between the radial size of galaxies and the radius of their host dark matter haloes from z similar to 0.1-3 using the Galaxy And Mass Assembly (GAMA) and Cosmic Assembly Near Infrared Deep Extragalactic Legacy Survey (CANDELS) surveys. We map dark matter halo mass to galaxy stellar mass using relationships from abundance matching, applied to the Bolshoi-Planck dissipationless N-body simulation. We define SRHR equivalent to r(e)/R-h as the ratio of galaxy radius to halo virial radius, and SRHR lambda equivalent to r(e)/(lambda R-h) as the ratio of galaxy radius to halo spin parameter times halo radius. At z similar to 0.1, we find an average value of SRHR similar or equal to 0.018 and SRHR. similar or equal to 0.5 with very little dependence on stellar mass. Stellar radius-halo radius (SRHR) and SRHR lambda have a weak dependence on cosmic time since z similar to 3. SRHR shows a mild decrease over cosmic time for low-mass galaxies, but increases slightly or does not evolve formoremassive galaxies. We find hints that at high redshift (z similar to 2-3), SRHR. is lower for more massive galaxies, while it shows no significant dependence on stellar mass at z less than or similar to 0.5. We find that for both the GAMA and CANDELS samples, at all redshifts from z similar to 0.1-3, the observed conditional size distribution in stellar mass bins is remarkably similar to the conditional distribution of lambda R-h. We discuss the physical interpretation and implications of these results
How Cosmic Web Environment Affects Galaxy Quenching Across Cosmic Time
We investigate how cosmic web structures affect galaxy quenching in the
IllustrisTNG (TNG-100) cosmological simulations by reconstructing the cosmic
web in each snapshot using the DisPerSE framework. We measure the distance from
each galaxy with stellar mass log(M*/Msun)>=8 to the nearest node (dnode) and
the nearest filament spine (dfil) and study the dependence of both median
specific star formation rate () and median gas fraction () on these
distances. We find that of galaxies is only dependent on cosmic web
environment at z<2, with the dependence increasing with time. At z<=0.5,
8<=log(M*/Msun)<9 galaxies are quenched at dnode<1 Mpc, and significantly star
formation-suppressed at dfil<1 Mpc, trends which are driven mostly by satellite
galaxies. At z of
log(M*/Msun)=10 galaxies
actually experience an upturn in at dnode<0.2 Mpc (this is caused by
both satellites and centrals). Much of this cosmic web-dependence of star
formation activity can be explained by the evolution in . Our results
suggest that in the past ~10 Gyr, low-mass satellites are quenched by rapid gas
stripping in dense environments near nodes and gradual gas starvation in
intermediate-density environments near filaments, while at earlier times cosmic
web structures efficiently channeled cold gas into most galaxies.
State-of-the-art ongoing spectroscopic surveys such as SDSS and DESI, as well
as those planned with JWST and Roman are required to test our predictions
against observations.Comment: 5 Figures, 15 pages, submitted to ApJ Letter
Filaments of The Slime Mold Cosmic Web And How They Affect Galaxy Evolution
We present a novel method for identifying cosmic web filaments using the
IllustrisTNG (TNG100) cosmological simulations and investigate the impact of
filaments on galaxies. We compare the use of cosmic density field estimates
from the Delaunay Tessellation Field Estimator (DTFE) and the Monte Carlo
Physarum Machine (MCPM), which is inspired by the slime mold organism, in the
DisPerSE structure identification framework. The MCPM-based reconstruction
identifies filaments with higher fidelity, finding more low-prominence/diffuse
filaments and better tracing the true underlying matter distribution than the
DTFE-based reconstruction. Using our new filament catalogs, we find that most
galaxies are located within 1.5-2.5 Mpc of a filamentary spine, with little
change in the median specific star formation rate and the median galactic gas
fraction with distance to the nearest filament. Instead, we introduce the
filament line density, {\Sigma}fil(MCPM), as the total MCPM overdensity per
unit length of a local filament segment, and find that this parameter is a
superior predictor of galactic gas supply and quenching. Our results indicate
that most galaxies are quenched and gas-poor near high-line density filaments
at z10.5 galaxies is mainly driven by
mass, while lower-mass galaxies are significantly affected by the filament line
density. In high-line density filaments, satellites are strongly quenched,
whereas centrals have reduced star formation, but not gas fraction, at z<=0.5.
We discuss the prospect of applying our new filament identification method to
galaxy surveys with SDSS, DESI, Subaru PFS, etc. to elucidate the effect of
large-scale structure on galaxy formation.Comment: Submitted to ApJ, comments welcome. Data available at
https://github.com/farhantasy/CosmicWeb-Galaxies
Clumpy Galaxies in CANDELS. I. The Definition of UV Clumps and the Fraction of Clumpy Galaxies at 0.5<z<3
Although giant clumps of stars are crucial to galaxy formation and evolution,
the most basic demographics of clumps are still uncertain, mainly because the
definition of clumps has not been thoroughly discussed. In this paper, we study
the basic demographics of clumps in star-forming galaxies (SFGs) at 0.5<z<3,
using our proposed physical definition that UV-bright clumps are discrete
star-forming regions that individually contribute more than 8% of the
rest-frame UV light of their galaxies. Clumps defined this way are
significantly brighter than the HII regions of nearby large spiral galaxies,
either individually or blended, when physical spatial resolution and
cosmological dimming are considered. Under this definition, we measure the
fraction of SFGs that contain at least one off-center clump (Fclumpy) and the
contributions of clumps to the rest-frame UV light and star formation rate of
SFGs in the CANDELS/GOODS-S and UDS fields, where our mass-complete sample
consists of 3239 galaxies with axial ratio q>0.5. The redshift evolution of
Fclumpy changes with the stellar mass (M*) of the galaxies. Low-mass
(log(M*/Msun)<9.8) galaxies keep an almost constant Fclumpy of about 60% from
z~3.0 to z~0.5. Intermediate-mass and massive galaxies drop their Fclumpy from
55% at z~3.0 to 40% and 15%, respectively, at z~0.5. We find that (1) the trend
of disk stabilization predicted by violent disk instability matches the Fclumpy
trend of massive galaxies; (2) minor mergers are a viable explanation of the
Fclumpy trend of intermediate-mass galaxies at z<1.5, given a realistic
observability timescale; and (3) major mergers are unlikely responsible for the
Fclumpy trend in all masses at z<1.5. The clump contribution to the rest-frame
UV light of SFGs shows a broad peak around galaxies with log(M*/Msun)~10.5 at
all redshifts, possibly linked to the molecular gas fraction of the galaxies.
(Abridged)Comment: 22 pages, 15 figures. Appeared in ApJ (2015, 800, 39). A few typos
correcte
Stellar Mass--Gas-phase Metallicity Relation at : A Power Law with Increasing Scatter toward the Low-mass Regime
We present the stellar mass ()--gas-phase metallicity relation (MZR)
and its scatter at intermediate redshifts () for 1381 field
galaxies collected from deep spectroscopic surveys. The star formation rate
(SFR) and color at a given of this magnitude-limited ( AB)
sample are representative of normal star-forming galaxies. For masses below
, our sample of 237 galaxies is 10 times larger than those
in previous studies beyond the local universe. This huge gain in sample size
enables superior constraints on the MZR and its scatter in the low-mass regime.
We find a power-law MZR at :
. Our MZR
shows good agreement with others measured at similar redshifts in the
literature in the intermediate and massive regimes, but is shallower than the
extrapolation of the MZRs of others to masses below . The SFR
dependence of the MZR in our sample is weaker than that found for local
galaxies (known as the Fundamental Metallicity Relation). Compared to a variety
of theoretical models, the slope of our MZR for low-mass galaxies agrees well
with predictions incorporating supernova energy-driven winds. Being robust
against currently uncertain metallicity calibrations, the scatter of the MZR
serves as a powerful diagnostic of the stochastic history of gas accretion, gas
recycling, and star formation of low-mass galaxies. Our major result is that
the scatter of our MZR increases as decreases. Our result implies that
either the scatter of the baryonic accretion rate or the scatter of the
-- relation increases as decreases. Moreover, our
measures of scatter at appears consistent with that found for local
galaxies.Comment: 18 pages, 10 figures. Accepted by ApJ. Typos correcte
The evolution of galaxy shapes in CANDELS: from prolate to oblate
We model the projected b/a-log a distributions of CANDELS main sequence
star-forming galaxies, where a (b) is the semi-major (semi-minor) axis of the
galaxy images. We find that smaller-a galaxies are rounder at all stellar
masses M and redshifts, so we include a when analyzing b/a distributions.
Approximating intrinsic shapes of the galaxies as triaxial ellipsoids and
assuming a multivariate normal distribution of galaxy size and two shape
parameters, we construct their intrinsic shape and size distributions to obtain
the fractions of prolate, oblate and spheroidal galaxies in each redshift and
mass bin. We find that galaxies tend to be prolate at low m and high redshifts,
and oblate at high M and low redshifts, qualitatively consistent with van der
Wel et al. (2014), implying that galaxies tend to evolve from prolate to
oblate. These results are consistent with the predictions from simulations
(Ceverino et al. 2015, Tomassetti et al. 2016) that the transition from prolate
to oblate is caused by a compaction event at a characteristic mass range,
making the galaxy center baryon dominated. We give probabilities of a galaxy's
being prolate, oblate or spheroidal as a function of its M, redshift, projected
b/a and a, which can facilitate target selections of galaxies with specific
shapes at hight redshifts. We also give predicted optical depths of galaxies,
which are qualitatively consistent with the expected correlation that AV should
be higher for edge-on disk galaxies in each log a slice at low redshift and
high mass bins.Comment: 24 pages, 25 figures, submitted to MNRA
Structural and Star-forming Relations since z similar to 3: Connecting Compact Star-forming and Quiescent Galaxies
We study the evolution of the scaling relations that compare the effective density (Sigma(e), r 9.6 -9.3M(circle dot) kpc(-2), allowing the most efficient identification of compact SFGs and quiescent galaxies at every redshift
The Epoch of Disk Settling: Z Approximately Equal to 1 to Now
We present evidence from a sample of 544 galaxies from the DEEP2 Survey for evolution of the internal kinematics of blue galaxies over 0.2 < z < 1.2. DEEP2 provides a large sample of high resolution galaxy spectra and dual-band Hubble imaging from which we measure emission-line kinematics and galaxy inclinations, respectively. Our large sample allows us to overcome scatter intrinsic to galaxy properties, in order to examine trends. At a fixed stellar mass, galaxies systematically decrease in disturbed motions and increase in rotation velocity and potential well depth with time. The most massive galaxies are the most well-ordered at all times, with higher rotation velocities and less disturbed motions compared to less massive galaxies. We quantify disturbed motions with an integrated gas velocity dispersion (sigma(sub g)), which is unlike the typical pressure-supported velocity dispersion measured for early type galaxies and galaxy bulges. Due to finite slit width and seeing, sigma(sub g) integrates over unresolved velocity gradients which can correspond to non-ordered gas kinematics such as small-scale velocity gradients, gas motions due to star-formation, or super-imposed clumps along the line-of-sight. We compile surveys of galaxy kinematics over 1.2 < z < 3.8 and do not find any trends with redshift, likely because these studies are biased toward the most highly star-forming systems. In summary, over the last approx 8 billion years since z = 1.2, blue galaxies evolve from disturbed to ordered systems as they settle to become the rotation-dominated disk galaxies observed in the Universe today, with the most massive galaxies always being the most evolved at any time
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