34 research outputs found
Revisiting the role of the Thermally-Pulsating Asymptotic Giant Branch phase in high-redshift galaxies
We study the debated contribution from thermally pulsing asymptotic giant
branch (TP-AGB) stars in evolutionary population synthesis models. We
investigate the Spectral Energy Distributions (SEDs) of a sample of 51
spectroscopically confirmed, high-z (), galaxies using
three evolutionary population synthesis models with strong, mild and light
TP-AGB. Our sample is the largest of spectroscopically confirmed galaxies on
which such models are tested so far. Galaxies were selected as passive, but we
model them using a variety of star formation histories in order not to be
dependent on this pre-selection.
We find that the observed SEDs are best fitted with a significant
contribution of TP-AGB stars or with substantial dust attenuation. Without
including reddening, TP-AGB-strong models perform better and deliver solutions
consistent within from the best-fit ones in the vast majority of
cases. Including reddening, all models perform similarly. Using independent
constraints from observations in the mid- and far-IR, we show that
low/negligible dust attenuation, i.e. , should be
preferred for the SEDs of passively-selected galaxies. Given that TP-AGB-light
models give systematically older ages for passive galaxies, we suggest number
counts of passive galaxies at higher redshifts as a further test to
discriminate among stellar population models.Comment: 48 pages, 17 figures, 10 Tables. Accepted for publication in MNRA
WFC3 grism confirmation of the distant cluster Cl J1449+0856 at z=2.00: Quiescent and star-forming galaxy populations
We present deep Hubble Space Telescope Wide Field Camera 3 slitless
spectroscopic observations of the distant cluster Cl J1449+0856. These cover a
single pointing with 18 orbits of G141 spectroscopy and F140W imaging, allowing
us to derive secure redshifts down to m_140~25.5 AB and 3sigma line fluxes of
5*10^(-18) erg/s/cm^2. In particular, we were able to spectroscopically confirm
12 early-type galaxies in the field up to z~3, 6 of which in the cluster core,
which represents the first direct spectroscopic confirmation of passive
galaxies in a z=2 cluster environment. With 140 redshifts in a ~6 arcmin^2
field, we can trace the spatial and redshift galaxy distribution in the cluster
core and background field. We find two strong peaks at z=2.00 and z=2.07, where
only one was seen in our previously published ground-based data. Thanks to the
spectroscopic confirmation of the cluster ETGs, we can now re-evaluate the
redshift of Cl J1449+0856 at z=2.00, rather than z=2.07, with the background
overdensity being revealed to be sparse and "sheet"-like. This presents an
interesting case of chance alignment of two close yet unrelated structures,
each one preferentially selected by different observing strategies. With 6
quiescent or early-type spectroscopic members and 20 star-forming ones, Cl
J1449+0856 is now reliably confirmed to be at z=2.00. The identified members
can now allow for a detailed study of galaxy properties in the densest
environment at z=2.Comment: 12 pages, 13 figure
Star-forming fractions and galaxy evolution with redshift in rich X-ray-selected galaxy clusters
We have compared stacked spectra of galaxies, grouped by environment and stellar mass, among 58 members of the redshift z = 1.24 galaxy cluster RDCS J1252.9-2927 (J1252.9) and 134 galaxies in the z = 0.84 cluster RX J0152.7-1357 (J0152.7). These two clusters are excellent laboratories to study how galaxies evolve from star-forming to passive at z ~ 1. We measured spectral indices and star-forming fractions for our density- and mass-based stacked spectra. The star-forming fraction among low-mass galaxies (<7 × 10^(10)M_⊙) is higher in J1252.9 than in J0152.7, at about 4σ significance. Thus star formation is being quenched between z = 1.24 and z = 0.84 for a substantial fraction of low-mass galaxies. Star-forming fractions were also found to be higher in J1252.9 in all environments, including the core. Passive galaxies in J1252.9 have systematically lower D_n4000 values than in J0152.7 in all density and mass groups, consistent with passive evolution at modestly super-solar metallicities
Clustering, host halos and environment of z2 galaxies as a function of their physical properties
Using a sample of 25683 star-forming and 2821 passive galaxies at ,
selected in the COSMOS field following the BzK color criterion, we study the
hosting halo mass and environment of galaxies as a function of their physical
properties. Spitzer and Herschel provide accurate SFR estimates for starburst
galaxies. We measure the auto- and cross-correlation functions of various
galaxy sub-samples and infer the properties of their hosting halos using both
an HOD model and the linear bias at large scale. We find that passive and
star-forming galaxies obey a similarly rising relation between the halo and
stellar mass. The mean host halo mass of star forming galaxies increases with
the star formation rate between 30 and 200 M.yr, but flattens
for higher values, except if we select only main-sequence galaxies. This
reflects the expected transition from a regime of secular co-evolution of the
halos and the galaxies to a regime of episodic starburst. We find similar large
scale biases for main-sequence, passive, and starburst galaxies at equal
stellar mass, suggesting that these populations live in halos of the same mass.
We detect an excess of clustering on small scales for passive galaxies and
showed, by measuring the large-scale bias of close pairs, that this excess is
caused by a small fraction () of passive galaxies being hosted by
massive halos ( M) as satellites. Finally,
extrapolating the growth of halos hosting the z2 population, we show that
M M galaxies at z2 will evolve, on average,
into massive (M M), field galaxies in the local
Universe and M M galaxies at z=2 into local,
massive, group galaxies. The most massive main-sequence galaxies and close
pairs of massive, passive galaxies end up in today's clusters.Comment: 18 pages, 16 figures, Accepted by A&
AGN Emission Line Diagnostics and the Mass-Metallicity Relation up to Redshift z~2: the Impact of Selection Effects and Evolution
Emission line diagnostic diagrams probing the ionization sources in galaxies,
such as the Baldwin-Phillips-Terlevich (BPT) diagram, have been used
extensively to distinguish AGN from purely star-forming galaxies. Yet, they
remain poorly understood at higher redshifts. We shed light on this issue with
an empirical approach based on a z~0 reference sample built from ~300,000 SDSS
galaxies, from which we mimic selection effects due to typical emission line
detection limits at higher redshift. We combine this low-redshift reference
sample with a simple prescription for luminosity evolution of the global galaxy
population to predict the loci of high-redshift galaxies on the BPT and
Mass-Excitation (MEx) diagnostic diagrams. The predicted bivariate
distributions agree remarkably well with direct observations of galaxies out to
z~1.5, including the observed stellar mass-metallicity (MZ) relation evolution.
As a result, we infer that high-redshift star-forming galaxies are consistent
with having "normal" ISM properties out to z~1.5, after accounting for
selection effects and line luminosity evolution. Namely, their optical line
ratios and gas-phase metallicities are comparable to that of low-redshift
galaxies with equivalent emission-line luminosities. In contrast, AGN
narrow-line regions may show a shift toward lower metallicities at higher
redshift. While a physical evolution of the ISM conditions is not ruled out for
purely star-forming galaxies, and may be more important starting at z>2, we
find that reliably quantifying this evolution is hindered by selections
effects. The recipes provided here may serve as a basis for future studies
toward this goal. Code to predict the loci of galaxies on the BPT and MEx
diagnostic diagrams, and the MZ relation as a function of emission line
luminosity limits, is made publicly available.Comment: Main article: 15 pages, 7 figures; Appendix: 13 pages, 11 figures.
Revisions: Paper now accepted for publication in the Astrophysical Journal
(same scientific content as previous arXiv version). IDL routines to make
empirical predictions on the BPT, MEx, and M-Z plane are now released at
https://sites.google.com/site/agndiagnostics/home/me
Compact, bulge dominated structures of spectroscopically confirmed quiescent galaxies at z~3
We study structural properties of spectroscopically confirmed massive
quiescent galaxies at with one of the first sizeable samples of
such sources, made of ten galaxies at
in the COSMOS field whose redshifts and quiescence are
confirmed by HST grism spectroscopy. Although affected by a weak bias toward
younger stellar populations, this sample is deemed to be largely representative
of the majority of the most massive and thus intrinsically rarest quiescent
sources at this cosmic time. We rely on targeted HST/WFC3 observations and fit
S\'ersic profiles to the galaxy surface brightness distributions at angstrom restframe. We find typically high S\'ersic indices and axis
ratios (medians and , respectively) suggesting that, at
odds with some previous results, the first massive quiescent galaxies may
largely be already bulge-dominated systems. We measure compact galaxy sizes
with an average of kpc at ,
in good agreement with the extrapolation at the highest masses of previous
determinations of the stellar mass - size relation of quiescent galaxies, and
of its redshift evolution, from photometrically selected samples at lower and
similar redshifts. This work confirms the existence of a population of compact,
bulge dominated, massive, quiescent sources at , providing one of
the first statistical estimates of their structural properties, and further
constraining the early formation and evolution of the first quiescent galaxies.Comment: 19 pages, 10 figures. Accepted for publication in MNRA
Feedback factory : multiple faint radio jets detected in a cluster at z=2
We report the detection of multiple faint radio sources, that we identify as active galactic nucleus (AGN) jets, within CLJ1449+0856 at z = 2 using 3 GHz Very Large Array observations. We study the effects of radio-jet-based kinetic feedback at high redshifts, which has been found to be crucial in low-redshift clusters to explain the observed thermodynamic properties of their intracluster medium (ICM). We investigate this interaction at an epoch featuring high levels of AGN activity and a transitional phase of ICM in regards to the likelihood of residual cold gas accretion. We measure a total flux of 30.6 +/- 3.3 mu Jy from the six detected jets. Their power contribution is estimated to be 1.2 (+/- 0.6) x 10(44) erg s(-1), although this value could be up to 4.7 x 10(44) erg s(-1). This is a factor of similar to 0.25-1.0 of the previously estimated instantaneous energy injection into the ICM of CLJ1449+0856 from AGN outflows and star formation that have already been found to be sufficient in globally offsetting the cooling flows in the cluster core. In line with the already detected abundance of star formation, this mode of feedback being distributed over multiple sites, contrary to a single central source observed at low redshifts, points to accretion of gas into the cluster centre. This also suggests a 'steady state' of the cluster featuring non-cool-core-like behaviour. Finally, we also examine the total infrared-radio luminosity ratio for the known sample of galaxies within the cluster core and find that dense environments do not have any serious consequence on the compliance of galaxies to the infrared-radio correlation.Peer reviewe
Accelerated structural evolution of galaxies in a starbursting cluster at z=2.51
Structural properties of cluster galaxies during their peak formation epoch,
provide key information on whether and how environment affects
galaxy formation and evolution. Based on deep HST/WFC3 imaging towards the
z=2.51 cluster, J1001, we explore environmental effects on the structure, color
gradients, and stellar populations of a statistical sample of cluster SFGs. We
find that the cluster SFGs are on average smaller than their field
counterparts. This difference is most pronounced at the high-mass end
() with nearly all of them lying below the
mass-size relation of field galaxies. The high-mass cluster SFGs are also
generally old with a steep negative color gradient, indicating an early
formation time likely associated with strong dissipative collapse. For low-mass
cluster SFGs, we unveil a population of compact galaxies with steep positive
color gradients that are not seen in the field. This suggests that the low-mass
compact cluster SFGs may have already experienced strong environmental effects,
e.g., tidal/ram pressure stripping, in this young cluster. These results
provide evidence on the environmental effects at work in the earliest formed
clusters with different roles in the formation of low and high-mass galaxies.Comment: 13 pages, 10 figures, 1 tabl
Revealing environmental dependence of molecular gas content in a distant X-ray cluster at z=2.51
We present a census of the molecular gas properties of galaxies in the most distant known X-ray cluster, CLJ1001, at z=2.51, using deep observations of CO(1-0) with JVLA. In total 14 cluster members with M∗>1010.5M⊙ are detected, including all the massive star-forming members within the virial radius, providing the largest galaxy sample in a single cluster at z>2 with CO(1-0) measurements. We find a large variety in the gas content of these cluster galaxies, which is correlated with their relative positions (or accretion states), with those closer to the cluster core being increasingly gas-poor. Moreover, despite their low gas content, the galaxies in the cluster center exhibit an elevated star formation efficiency (SFE=SFR/Mgas) compared to field galaxies, suggesting that the suppression on the SFR is likely delayed compared to that on the gas content. Their gas depletion time is around tdep∼400 Myrs, comparable to the cluster dynamical time. This implies that they will likely consume all their gas within a single orbit around the cluster center, and form a passive cluster core by z∼2. This result is one of the first direct pieces of evidence for the influence of environment on the gas reservoirs and SFE of z>2 cluster galaxies, thereby providing new insights into the rapid formation and quenching of the most massive galaxies in the early universe