313 research outputs found
The CANDELS/SHARDS Multiwavelength Catalog in GOODS-N: Photometry, Photometric Redshifts, Stellar Masses, Emission-line Fluxes, and Star Formation Rates
We present a WFC3 F160W (H-band) selected catalog in the CANDELS/GOODS-N field containing photometry from the ultraviolet (UV) to the far-infrared (IR), photometric redshifts, and stellar parameters derived from the analysis of the multiwavelength data. The catalog contains 35,445 sources over the 171 arcmin^2 of the CANDELS F160W mosaic. The 5Ï detection limits (within an aperture of radius 0.â17) of the mosaic range between H = 27.8, 28.2, and 28.7 in the wide, intermediate, and deep regions, which span approximately 50%, 15%, and 35% of the total area. The multiwavelength photometry includes broadband data from the UV (U band from KPNO and LBC), optical (HST/ACS F435W, F606W, F775W, F814W, and F850LP), near-to-mid IR (HST/WFC3 F105W, F125W, F140W, and F160W; Subaru/MOIRCS Ks; CFHT/Megacam K; and Spitzer/IRAC 3.6, 4.5, 5.8, and 8.0 ÎŒm), and far-IR (Spitzer/MIPS 24 ÎŒm, HERSCHEL/PACS 100 and 160 ÎŒm, SPIRE 250, 350 and 500 ÎŒm) observations. In addition, the catalog also includes optical medium-band data (R ~ 50) in 25 consecutive bands, λ = 500â950 nm, from the SHARDS survey and WFC3 IR spectroscopic observations with the G102 and G141 grisms (R ~ 210 and 130). The use of higher spectral resolution data to estimate photometric redshifts provides very high, and nearly uniform, precision from z = 0â2.5. The comparison to 1485 good-quality spectroscopic redshifts up to z ~ 3 yields Îz/(1 + z_(spec)) = 0.0032 and an outlier fraction of η = 4.3%. In addition to the multiband photometry, we release value-added catalogs with emission-line fluxes, stellar masses, dust attenuations, UV- and IR-based star formation rates, and rest-frame colors
Half-mass radii for ~7,000 galaxies at 1.0 < z < 2.5: most of the evolution in the mass-size relation is due to color gradients
Radial mass-to-light ratio gradients cause the half-mass and half-light radii
of galaxies to differ, potentially biasing studies that use half-light radii.
Here we present the largest catalog to date of galaxy half-mass radii at z > 1:
7,006 galaxies in the CANDELS fields at 1.0 < z < 2.5. The sample includes both
star-forming and quiescent galaxies with stellar masses 9.0 < log(M_* /
M_\odot) < 11.5. We test three methods for calculating half-mass radii from
multi-band PSF-matched HST imaging: two based on spatially-resolved SED
modeling, and one that uses a rest-frame color profile. All three methods
agree, with scatter <~0.3 dex. In agreement with previous studies, most
galaxies in our sample have negative color gradients (the centers are redder
than the outskirts, and r_e,mass < r_e,light). We find that color gradient
strength has significant trends with increasing stellar mass, half-light
radius, U-V color, and stellar mass surface density. These trends have not been
seen before at z>1. Furthermore, color gradients of star-forming and quiescent
galaxies show a similar redshift evolution: they are flat at z>~2, then steeply
decrease as redshift decreases. This affects the galaxy mass-size relation. The
normalizations of the star-forming and quiescent r_mass-M_* relations are
10-40% smaller than the corresponding r_light-M_* relations; the slopes are
~0.1-0.3 dex shallower. Finally, the half-mass radii of star-forming and
quiescent galaxies at M_* = 10^{10.5}M_\odot only grow by ~1%$ and ~8% between
z~2.25 and z~1.25. This is significantly less than the ~37% and ~47% size
increases found when using the half-light radius.Comment: 18 pages, 10 figures. Accepted to Ap
The CANDELS/SHARDS Multiwavelength Catalog in GOODS-N: Photometry, Photometric Redshifts, Stellar Masses, Emission-line Fluxes, and Star Formation Rates
We present a WFC3 F160W (H-band) selected catalog in the CANDELS/GOODS-N field containing photometry from the ultraviolet (UV) to the far-infrared (IR), photometric redshifts, and stellar parameters derived from the analysis of the multiwavelength data. The catalog contains 35,445 sources over the 171 arcmin^2 of the CANDELS F160W mosaic. The 5Ï detection limits (within an aperture of radius 0.â17) of the mosaic range between H = 27.8, 28.2, and 28.7 in the wide, intermediate, and deep regions, which span approximately 50%, 15%, and 35% of the total area. The multiwavelength photometry includes broadband data from the UV (U band from KPNO and LBC), optical (HST/ACS F435W, F606W, F775W, F814W, and F850LP), near-to-mid IR (HST/WFC3 F105W, F125W, F140W, and F160W; Subaru/MOIRCS Ks; CFHT/Megacam K; and Spitzer/IRAC 3.6, 4.5, 5.8, and 8.0 ÎŒm), and far-IR (Spitzer/MIPS 24 ÎŒm, HERSCHEL/PACS 100 and 160 ÎŒm, SPIRE 250, 350 and 500 ÎŒm) observations. In addition, the catalog also includes optical medium-band data (R ~ 50) in 25 consecutive bands, λ = 500â950 nm, from the SHARDS survey and WFC3 IR spectroscopic observations with the G102 and G141 grisms (R ~ 210 and 130). The use of higher spectral resolution data to estimate photometric redshifts provides very high, and nearly uniform, precision from z = 0â2.5. The comparison to 1485 good-quality spectroscopic redshifts up to z ~ 3 yields Îz/(1 + z_(spec)) = 0.0032 and an outlier fraction of η = 4.3%. In addition to the multiband photometry, we release value-added catalogs with emission-line fluxes, stellar masses, dust attenuations, UV- and IR-based star formation rates, and rest-frame colors
Testing the Recovery of Intrinsic Galaxy Sizes and Masses of z~2 Massive Galaxies Using Cosmological Simulations
Accurate measurements of galaxy masses and sizes are key to tracing galaxy
evolution over time. Cosmological zoom-in simulations provide an ideal test bed
for assessing the recovery of galaxy properties from observations. Here, we
utilize galaxies with at z~1.7-2 from the
MassiveFIRE cosmological simulation suite, part of the Feedback in Realistic
Environments (FIRE) project. Using mock multi-band images, we compare intrinsic
galaxy masses and sizes to observational estimates. We find that observations
accurately recover stellar masses, with a slight average underestimate of ~0.06
dex and a ~0.15 dex scatter. Recovered half-light radii agree well with
intrinsic half-mass radii when averaged over all viewing angles, with a
systematic offset of ~0.1 dex (with the half-light radii being larger) and a
scatter of ~0.2 dex. When using color gradients to account for mass-to-light
variations, recovered half-mass radii also exceed the intrinsic half-mass radii
by ~0.1 dex. However, if not properly accounted for, aperture effects can bias
size estimates by ~0.1 dex. No differences are found between the mass and size
offsets for star-forming and quiescent galaxies. Variations in viewing angle
are responsible for ~25% of the scatter in the recovered masses and sizes. Our
results thus suggest that the intrinsic scatter in the mass-size relation may
have previously been overestimated by ~25%. Moreover, orientation-driven
scatter causes the number density of very massive galaxies to be overestimated
by ~0.5 dex at .Comment: Published in the Astrophysical Journal Letters (7 pages, 5 figures;
updated to match published version
Color gradients along the quiescent galaxy sequence: clues to quenching and structural growth
This Letter examines how the sizes, structures, and color gradients of
galaxies change along the quiescent sequence. Our sample consists of ~400
quiescent galaxies at and
in three CANDELS fields. We exploit deep multi-band HST imaging to derive
accurate mass profiles and color gradients, then use an empirical calibration
from rest-frame UVJ colors to estimate galaxy ages. We find that -- contrary to
previous results -- the youngest quiescent galaxies are not significantly
smaller than older quiescent galaxies at fixed stellar mass. These
`post-starburst' galaxies only appear smaller in half-light radii because they
have systematically flatter color gradients. The strength of color gradients in
quiescent galaxies is a clear function of age, with older galaxies exhibiting
stronger negative color gradients (i.e., redder centers). Furthermore, we find
that the central mass surface density is independent of age at fixed
stellar mass, and only weakly depends on redshift. This finding implies that
the central mass profiles of quiescent galaxies do not significantly change
with age; however, we find that older quiescent galaxies have additional mass
at large radii. Our results support the idea that building a massive core is a
necessary requirement for quenching beyond , and indicate that
post-starburst galaxies are the result of a rapid quenching process that
requires structural change. Furthermore, our observed color gradient and mass
profile evolution supports a scenario where quiescent galaxies grow inside-out
via minor mergers.Comment: 7 pages, 5 figures. Accepted to ApJ
Keck-I MOSFIRE Spectroscopy of Compact Star-forming Galaxies at z âł 2: 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 2 †z †2.5 with star formation rates of SFR ~ 100 M_â yr^(â1) and masses of log(M/M_â) ~10.8. Their high integrated gas velocity dispersions of Ï_(int_ =230^(+40)_(-30) km s^(â1), as measured from emission lines of Hα and [O III], and the resultant M_* -Ï_(int) relation and M_*-M_(dyn) all match well to those of compact quiescent galaxies at z ~ 2, as measured from stellar absorption lines. Since log(M*/M_(dyn)) =â0.06 ± 0.2 dex, these compact SFGs appear to be dynamically relaxed and evolved, i.e., depleted in gas and dark matter (<13^(+17)_(-13)%), and present larger Ï_(int) 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 z âł 2 are already losing gas to become the immediate progenitors of compact quiescent galaxies by z ~ 2
Evolution of the anti-truncated stellar profiles of S0 galaxies since in the SHARDS survey: I - Sample and Methods
The controversy about the origin of the structure of S0--E/S0 galaxies may be
due to the difficulty of comparing surface brightness profiles with different
depths, photometric corrections and PSF effects (almost always ignored). We aim
to quantify the properties of Type-III (anti-truncated) discs in a sample of S0
galaxies at 0.2<z<0.6. In this paper, we present the sample selection and
describe in detail the methods to robustly trace the structure in their
outskirts and correct for PSF effects. We have selected and classified a sample
of 150 quiescent galaxies at 0.2<z<0.6 in the GOODS-N field. We perform a
quantitative structural analysis of 44 S0-E/S0 galaxies. We corrected their
surface brightness profiles for PSF distortions and analysed the biases in the
structural and photometric parameters when the PSF correction is not applied.
Additionally, we have developed Elbow, an automatic statistical method to
determine whether a possible break is significant - or not - and its type and
made it publicly available. We found 14 anti-truncated S0-E/S0 galaxies in the
range 0.2<z<0.6 (~30% of the final sample). This fraction is similar to the
those reported in the local Universe. In our sample, ~25% of the Type-III
breaks observed in PSF-uncorrected profiles are artifacts, and their profiles
turn into a Type I after PSF correction. PSF effects also soften Type-II
profiles. We found that the profiles of Type-I S0 and E/S0 galaxies of our
sample are compatible with the inner profiles of the Type-III, in contrast with
the outer profiles. We have obtained the first robust and reliable sample of 14
anti-truncated S0--E/S0 galaxies beyond the local Universe, in the range
0.2<z<0.6. PSF effects significantly affect the shape of the surface brightness
profiles in galaxy discs even in the case of the narrow PSF of HST/ACS images,
so future studies on the subject should make an effort to correct them.Comment: Accepted for publishing in Astronomy & Astrophysics. 75 pages, 57
figure
Spitzer view on the downsizing scenario of galaxy formation and the role of AGN
We present the latest results of the Spitzer Cosmological Surveys concerning the characterization of the evolution of galaxies in the last 12 Gyr (from z=4). We have analyzed the stellar mass function up to z=4 using a sample of more the 28,000 galaxies selected in the rest-frame near-infrared with Spitzer/IRAC. Our results confirm and quantify the âdownsizingâ scenario of galaxy formation. Based on the study of the specific SFRs of X-ray emitters, we discuss the role of AGN in the evolution of galaxies, arguing against the link between nuclear activity and the quenching of the star formation in massive galaxies at z<1.4
Exploring the evolutionary paths of the most massive galaxies since z~2
We use Spitzer MIPS data from the FIDEL Legacy Project in the Extended Groth
Strip to analyze the stellar mass assembly of massive (M>10^11 M_sun) galaxies
at z<2 as a function of structural parameters. We find 24 micron emission for
more than 85% of the massive galaxies morphologically classified as disks, and
for more than 57% of the massive systems morphologically classified as
spheroids at any redshift, with about 8% of sources harboring a bright X-ray
and/or infrared emitting AGN. More noticeably, 60% of all compact massive
galaxies at z=1-2 are detected at 24 micron, even when rest-frame optical
colors reveal that they are dead and evolving passively. For spheroid-like
galaxies at a given stellar mass, the sizes of MIPS non-detections are smaller
by a factor of 1.2 in comparison with IR-bright sources. We find that disk-like
massive galaxies present specific SFRs ranging from 0.04 to 0.2 Gyr^-1 at z<1
(SFRs ranging from 1 to 10 M_sun/yr), typically a factor of 3-6 higher than
massive spheroid-like objects in the same redshift range. At z>1, and more
pronouncedly at z>1.3, the median specific SFRs of the disks and spheroids
detected by MIPS are very similar, ranging from 0.1 to 1 Gyr^-1 (SFR=10-200
M_sun/yr). We estimate that massive spheroid-like galaxies may have doubled (at
the most) their stellar mass from star-forming events at z<2: less than 20%
mass increase at 1.7<z<2.0, up to 40% more at 1.1<z<1.7, and less than 20%
additional increase at z<1. Disk-like galaxies may have tripled (at the most)
their stellar mass at z<2 from star formation alone: up to 40% mass increase at
1.7<z<2.0, and less than 180% additional increase below z=1.7 occurred at a
steady rate.Comment: Accepted for publication in ApJ; 10 pages, 5 figures, 1 tabl
The galaxy major merger fraction to z ~ 1
Aims. The importance of disc-disc major mergers in galaxy evolution remains uncertain. We study the major merger fraction in a SPITZER/IRAC-selected catalogue in the GOODS-S field up to z ~ 1 for luminosity- and mass-limited samples. Methods. We select disc-disc merger remnants on the basis of morphological asymmetries/distortions, and address three main sources of systematic errors: (i) we explicitly apply morphological K-corrections; (ii) we measure asymmetries in galaxies artificially redshifted to z_d = 1.0 to deal with loss of morphological information with redshift; and (iii) we take into account the observational errors in z and A, which tend to overestimate the merger fraction, though use of maximum likelihood techniques. Results. We obtain morphological merger fractions (f_m^mph) below 0.06 up to z ~ 1. Parameterizing the merger fraction evolution with redshift as f_m^mph (z) = f_m^mph (0)(1 + z)^m, we find that m = 1.8 ± 0.5 for M(B)†-20 galaxies, while m = 5.4 ± 0.4 for M_* â„ 10^10 M_âš galaxies. When we translate our merger fractions to merger rates (R_m^mph), their evolution, parameterized as R_m^mph (z) = R_m^mph (0)(1+ z)^n, is quite similar in both cases: n = 3.3 ± 0.8 for M(B) †-20 galaxies, and n = 3.5 ± 0.4 for M_* â„10^10 M_âš galaxies. Conclusions. Our results imply that only similar to 8% of today's M(star) â„ 10^10 M_âš galaxies have undergone a disc-disc major merger since z ~ 1. In addition, ~ 21% of M_* â„ 10(10) M_âš galaxies at z ~ 1 have undergone one of these mergers since z similar to 1.5. This suggests that disc-disc major mergers are not the dominant process in the evolution of M_* â„ 10(10) M_âš galaxies since z 1, with only 0.2 disc-disc major mergers per galaxy, but may be an important process at z > 1, with ~ 1 merger per galaxy at 1 < z < 3
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