Abstract
The Cosmic Evolution Survey (COSMOS) has become a cornerstone of extragalactic astronomy. Since the last public catalog in 2015, a wealth of new imaging and spectroscopic data have been ...collected in the COSMOS field. This paper describes the collection, processing, and analysis of these new imaging data to produce a new reference photometric redshift catalog. Source detection and multiwavelength photometry are performed for 1.7 million sources across the 2 deg
2
of the COSMOS field, ∼966,000 of which are measured with all available broadband data using both traditional aperture photometric methods and a new profile-fitting photometric extraction tool,
The Farmer
, which we have developed. A detailed comparison of the two resulting photometric catalogs is presented. Photometric redshifts are computed for all sources in each catalog utilizing two independent photometric redshift codes. Finally, a comparison is made between the performance of the photometric methodologies and of the redshift codes to demonstrate an exceptional degree of self-consistency in the resulting photometric redshifts. The
i
< 21 sources have subpercent photometric redshift accuracy and even the faintest sources at 25 <
i
< 27 reach a precision of 5%. Finally, these results are discussed in the context of previous, current, and future surveys in the COSMOS field. Compared to COSMOS2015, it reaches the same photometric redshift precision at almost one magnitude deeper. Both photometric catalogs and their photometric redshift solutions and physical parameters will be made available through the usual astronomical archive systems (ESO Phase 3, IPAC-IRSA, and CDS).
Abstract
We derive 2D dust attenuation maps at ∼1 kpc resolution from the UV continuum for 10 galaxies on the
z
∼ 2 star-forming main sequence (SFMS). Comparison with IR data shows that 9 out of 10 ...galaxies do not require further obscuration in addition to the UV-based correction, though our sample does not include the most heavily obscured, massive galaxies. The individual rest-frame
V
-band dust attenuation (
A
V
) radial profiles scatter around an average profile that gently decreases from ∼1.8 mag in the center down to ∼0.6 mag at ∼3–4 half-mass radii. We use these maps to correct UV- and H
α
-based star formation rates (SFRs), which agree with each other. At masses
, the dust-corrected specific SFR (sSFR) profiles are on average radially constant at a mass-doubling timescale of ∼300 Myr, pointing at a synchronous growth of bulge and disk components. At masses
, the sSFR profiles are typically centrally suppressed by a factor of ∼10 relative to the galaxy outskirts. With total central obscuration disfavored, this indicates that at least a fraction of massive
z
∼ 2 SFMS galaxies have started their inside-out star formation quenching that will move them to the quenched sequence. In combination with other observations, galaxies above and below the ridge of the SFMS relation have, respectively, centrally enhanced and centrally suppressed sSFRs relative to their outskirts, supporting a picture where bulges are built owing to gas “compaction” that leads to a high central SFR as galaxies move toward the upper envelope of the SFMS.
The Cosmic Evolution Survey (COSMOS) is designed to probe the correlated evolution of galaxies, star formation, active galactic nuclei (AGNs), and dark matter (DM) with large-scale structure (LSS) ...over the redshift range z > 0.5-6. The survey includes multiwavelength imaging and spectroscopy from X-ray-to-radio wavelengths covering a 2 deg super(2) area, including HST imaging. Given the very high sensitivity and resolution of these data sets, COSMOS also provides unprecedented samples of objects at high redshift with greatly reduced cosmic variance, compared to earlier surveys. Here we provide a brief overview of the survey strategy, the characteristics of the major COSMOS data sets, and a summary the science goals.
Most present-day galaxies with stellar masses ≥1011 solar masses show no ongoing star formation and are dense spheroids. Ten billion years ago, similarly massive galaxies were typically forming stars ...at rates of hundreds solar masses per year. It is debated how star formation ceased, on which time scales, and how this "quenching" relates to the emergence of dense spheroids. We measured stellar mass and star-formation rate surface density distributions in star-forming galaxies at redshift 2.2 with ∼1-kiloparsec resolution. We find that, in the most massive galaxies, star formation is quenched from the inside out, on time scales less than 1 billion years in the inner regions, up to a few billion years in the outer disks. These galaxies sustain high star-formation activity at large radii, while hosting fully grown and already quenched bulges in their cores.
ABSTRACT
The physical properties of galactic winds are one of the keys to understand galaxy formation and evolution. These properties can be constrained thanks to background quasar lines of sight ...(LOS) passing near star-forming galaxies (SFGs). We present the first results of the MusE GAs FLOw and Wind survey obtained from two quasar fields, which have eight Mg
ii
absorbers of which three have rest equivalent width greater than 0.8 Å. With the new Multi Unit Spectroscopic Explorer (MUSE) spectrograph on the Very Large Telescope (VLT), we detect six (75%) Mg
ii
host galaxy candidates within a radius of 30″ from the quasar LOS. Out of these six galaxy–quasar pairs, from geometrical argument, one is likely probing galactic outflows, where two are classified as “ambiguous,” two are likely probing extended gaseous disks and one pair seems to be a merger. We focus on the wind-pair and constrain the outflow using a high-resolution quasar spectra from the Ultraviolet and Visual Echelle Spectrograph. Assuming the metal absorption to be due to ga;s flowing out of the detected galaxy through a cone along the minor axis, we find outflow velocities in the order of ≈150
(i.e., smaller than the escape velocity) with a loading factor,
, of ≈0.7. We see evidence for an open conical flow, with a low-density inner core. In the future, MUSE will provide us with about 80 multiple galaxy−quasar pairs in two dozen fields.
We use the large COSMOS sample of galaxies to study in an internally self-consistent way the change in the number densities of quenched early-type galaxies (Q-ETGs) of a given size over the redshift ...interval 0.2 < z < 1 in order to study the claimed size evolution of these galaxies. In a stellar mass bin at 10 super(10.5) < M sub(galaxy) < 10 super(11) M sub(middot in circle), we see no change in the number density of compact Q-ETGs over this redshift range, while in a higher mass bin at >10 super(11) M sub(middot in circle), where we would expect merging to be more significant, we find a small decrease, by ~30%. In both mass bins, the increase of the median sizes of Q-ETGs with time is primarily caused by the addition to the size function of larger and more diffuse Q-ETGs. At all masses, compact Q-ETGs become systematically redder toward later epochs, with a (U - V) color difference which is consistent with a passive evolution of their stellar populations, indicating that they are a stable population that does not appreciably evolve in size. We find furthermore, at all epochs, that the larger Q-ETGs (at least in the lower mass bin) have average rest-frame colors that are systematically bluer than those of the more compact Q-ETGs, suggesting that the former are indeed younger than the latter. The idea that new, large, Q-ETGs are responsible for the observed growth in the median size of the population at a given mass is also supported by analysis of the sizes and number of the star-forming galaxies that are expected to be the progenitors of the new Q-ETGs over the same period. In the low mass bin, the new Q-ETGs appear to have similar to 30% smaller half-light radii than their star-forming progenitors. This is likely due to the fading of their disks after they cease star formation. Comparison with higher redshifts shows that the median size of newly quenched galaxies roughly scales, at constant mass, as (1 + z) super(-1). We conclude that the dominant cause of the size evolution seen in the Q-ETG population is that the average sizes and thus stellar densities of individual Q-ETGs roughly scale with the average density of the universe at the time when they were quenched, and that subsequent size changes in individual objects, through merging or other processes, are of secondary importance, especially at masses below 10 super(11) M sub(middot in circle).
Abstract
We investigate the relationship between star formation activity and outflow properties on kiloparsec scales in a sample of 28 star-forming galaxies at
z
∼ 2–2.6, using adaptive optics ...assisted integral field observations from SINFONI on the Very Large Telescope. The narrow and broad components of the H
α
emission are used to simultaneously determine the local star formation rate surface density (
), and the outflow velocity
and mass outflow rate
, respectively. We find clear evidence for faster outflows with larger mass loading factors at higher
. The outflow velocities scale as
∝
0.34±0.10
, which suggests that the outflows may be driven by a combination of mechanical energy released by supernova explosions and stellar winds, as well as radiation pressure acting on dust grains. The majority of the outflowing material does not have sufficient velocity to escape from the galaxy halos, but will likely be re-accreted and contribute to the chemical enrichment of the galaxies. In the highest
regions the outflow component contains an average of ∼45% of the H
α
flux, while in the lower
regions only ∼10% of the H
α
flux is associated with outflows. The mass loading factor,
η
=
/SFR, is positively correlated with
but is relatively low even at the highest
:
η
≲ 0.5 × (380 cm
−3
/
n
e
). This may be in tension with the
η
≳ 1 required by cosmological simulations, unless a significant fraction of the outflowing mass is in other gas phases and has sufficient velocity to escape the galaxy halos.
We present a census of ionized gas outflows in 599 normal galaxies at redshift 0.6 < z < 2.7, mostly based on integral field spectroscopy of Hα, N ii, and S ii line emission. The sample fairly ...homogeneously covers the main sequence of star-forming galaxies with masses 9.0 < log(M */M ⊙) < 11.7, and probes into the regimes of quiescent galaxies and starburst outliers. About one-third exhibits the high-velocity component indicative of outflows, roughly equally split into winds driven by star formation (SF) and active galactic nuclei (AGNs). The incidence of SF-driven winds correlates mainly with SF properties. These outflows have typical velocities of ∼450 km s−1, local electron densities of n e ∼ 380 cm−3, modest mass loading factors of ∼0.1–0.2 at all galaxy masses, and energetics compatible with momentum driving by young stellar populations. The SF-driven winds may escape from log(M */M ⊙) ≲ 10.3 galaxies, but substantial mass, momentum, and energy in hotter and colder outflow phases seem required to account for low galaxy formation efficiencies in the low-mass regime. Faster AGN-driven outflows (∼1000–2000 km s−1) are commonly detected above log(M */M ⊙) ∼ 10.7, in up to ∼75% of log(M */M ⊙) ≳ 11.2 galaxies. The incidence, strength, and velocity of AGN-driven winds strongly correlates with stellar mass and central concentration. Their outflowing ionized gas appears denser (n e ∼ 1000 cm−3), and possibly compressed and shock-excited. These winds have comparable mass loading factors as the SF-driven winds but carry ∼10 (∼50) times more momentum (energy). The results confirm our previous findings of high-duty-cycle, energy-driven outflows powered by AGN above the Schechter mass, which may contribute to SF quenching.
ABSTRACT
We investigate if the discrepancy between estimates of the total baryon mass fraction obtained from observations of the cosmic microwave background (CMB) and of galaxy groups/clusters ...persists when a large sample of groups is considered. To this purpose, 91 candidate X-ray groups/poor clusters at redshift 0.1 ⩽
z
⩽ 1 are selected from the COSMOS 2 deg
2
survey, based only on their X-ray luminosity and extent. This sample is complemented by 27 nearby clusters with a robust, analogous determination of the total and stellar mass inside
R
500
. The total sample of 118 groups and clusters with
z
⩽ 1 spans a range in
M
500
of ∼10
13
–10
15
M
☉
. We find that the stellar mass fraction associated with galaxies at
R
500
decreases with increasing total mass as
M
−0.37 ± 0.04
500
, independent of redshift. Estimating the total gas mass fraction from a recently derived, high-quality scaling relation, the total baryon mass fraction (
f
stars+gas
500
=
f
stars
500
+
f
gas
500
) is found to increase by ∼25%, when
M
500
increases from 〈
M
〉 = 5 × 10
13
M
☉
to 〈
M
〉 = 7 × 10
14
M
☉
. After consideration of a plausible contribution due to intracluster light (11%–22% of the total stellar mass) and gas depletion through the hierarchical assembly process (10% of the gas mass), the estimated values of the total baryon mass fraction are still lower than the latest CMB measure of the same quantity (WMAP5), at a significance level of 3.3σ for groups of 〈
M
〉 = 5 × 10
13
M
☉
. The discrepancy decreases toward higher total masses, such that it is 1σ at 〈
M
〉 = 7 × 10
14
M
☉
. We discuss this result in terms of nongravitational processes such as feedback and filamentary heating.
Photo-z performance for precision cosmology Bordoloi, R.; Lilly, S. J.; Amara, A.
Monthly notices of the Royal Astronomical Society,
August 2010, Letnik:
406, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Current and future weak-lensing surveys will rely on photometrically estimated redshifts of very large numbers of galaxies. In this paper, we address several different aspects of the demanding ...photo-z performance that will be required for future experiments, such as the proposed ESA Euclid mission. It is first shown that the proposed all-sky near-infrared photometry from Euclid, in combination with anticipated ground-based photometry (e.g. PanStarrs-2 or DES) should yield the required precision in individual photo-z of σz(z) ≤ 0.05(1 +z) at IAB≤ 24.5. Simple a priori rejection schemes based on the photometry alone can be tuned to recognize objects with wildly discrepant photo-z and to reduce the outlier fraction to ≤0.25 per cent with only modest loss of otherwise usable objects. Turning to the more challenging problem of determining the mean redshift 〈z〉 of a set of galaxies to a precision of |Δ〈z〉| ≤ 0.002(1 +z) we argue that, for many different reasons, this may be best accomplished by relying on the photo-z themselves rather than on the direct measurement of 〈z〉 from spectroscopic redshifts of a representative subset of the galaxies, as has usually been envisaged. We present in Appendix A an analysis of the substantial difficulties in the latter approach that arise from the presence of large-scale structure in spectroscopic survey fields. A simple adaptive scheme based on the statistical properties of the photo-z likelihood functions is shown to meet this stringent systematic requirement, although further tests on real data will be required to verify this. We also examine the effect of an imprecise correction for Galactic extinction on the photo-z and the precision with which the Galactic extinction can be determined from the photometric data itself, for galaxies with or without spectroscopic redshifts. We also explore the effects of contamination by fainter overlapping objects in photo-z determination. The overall conclusion of this paper is that the acquisition of photometrically estimated redshifts with the precision required for Euclid, or other similar experiments, will be challenging but possible.
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