Context. There is now a large consensus that the current epoch of the cosmic star formation history (CSFH) is dominated by low mass galaxies while the most active phase, between redshifts 1 and 2, is ...dominated by more massive galaxies, which evolve more quickly. Aims. Massive galaxies tend to inhabit very massive haloes, such as galaxy groups and clusters. We aim to understand whether the observed “galaxy downsizing” could be interpreted as a “halo downsizing”, whereas the most massive haloes, and their galaxy populations, evolve more rapidly than the haloes with lower mass. Methods. We studied the contribution to the CSFH of galaxies inhabiting group-sized haloes. This is done through the study of the evolution of the infra-red (IR) luminosity function of group galaxies from redshift 0 to redshift ~1.6. We used a sample of 39 X-ray-selected groups in the Extended Chandra Deep Field South (ECDFS), the Chandra Deep Field North (CDFN), and the COSMOS field, where the deepest available mid- and far-IR surveys have been conducted with Spitzer MIPS and with the Photodetector Array Camera and Spectrometer (PACS) on board the Herschel satellite. Results. Groups at low redshift lack the brightest, rarest, and most star forming IR-emitting galaxies observed in the field. Their IR-emitting galaxies contribute ≤10% of the comoving volume density of the whole IR galaxy population in the local Universe. At redshift ≳1, the most IR-luminous galaxies (LIRGs and ULIRGs) are mainly located in groups, and this is consistent with a reversal of the star formation rate (SFR) vs. density anti-correlation observed in the nearby Universe. At these redshifts, group galaxies contribute 60–80% of the CSFH, i.e. much more than at lower redshifts. Below z ~ 1, the comoving number and SFR densities of IR-emitting galaxies in groups decline significantly faster than those of all IR-emitting galaxies. Conclusions. Our results are consistent with a “halo downsizing” scenario and highlight the significant role of “environment” quenching in shaping the CSFH.
Context. Dust attenuation curves in external galaxies are useful for studying their dust properties as well as interpreting their intrinsic spectral energy distributions. These functions are not very ...well known in the UV range whether at low or high redshift. In particular, the presence or absence of a UV bump at 2175 Å remains an open issue that has consequences on the interpretation of broad band colours of galaxies involving the UV range. Aims. We want to study the dust attenuation curve in the UV range at z > 1 where the UV is redshifted into the visible and with Herschel data to constrain dust emission and a global dust attenuation. In particular, we search for a UV bump and related implications for dust attenuation determinations. Methods. We use deep photometric data of the Chandra Deep Field South obtained with intermediate and broad band filters by the MUSYC project to sample the UV rest frame of galaxies with 1 < z < 2. Herschel/PACS and Spitzer/MIPS data are used to measure the dust emission. We select 30 galaxies with high S/N in all bands. Their SEDs from the UV to the far-IR are fitted using the CIGALE code and the characteristics of the dust attenuation curves obtained as Bayesian outputs of the SED fitting process. Results. The mean dust attenuation curve we derive exhibits a significant UV bump at 2175 Å whose amplitude corresponds to 35% (76%) that of the Milky Way (Large Magellanic Cloud: LMC2 supershell) extinction curve. An analytical expression of the average attenuation curve (A(λ)/AV) is given and found to be slightly steeper than the Calzetti et al. one, although at a 1σ level. Our galaxy sample is used to study the derivation of the slopes of the UV continuum from broad band colours, including the rest frame GALEX FUV − NUV colour. Systematic errors induced by the presence of the bump are quantified. We compare dust attenuation factors measured with CIGALE to the slope of the UV continuum and find that there is a large scatter around the relation valid for local starbursts (~0.7 mag). The uncertainties on the determination of the UV slope lead to an extra systematic error in a range of 0.3 to 0.7 mag on dust attenuation when a filter overlaps the UV bump.
Star formation (SF) in the galaxy populations of local massive clusters is reduced with respect to field galaxies, and tends to be suppressed in the core region. Indications of a reversal of the ...SF-density relation have been observed in a few z > 1.4 clusters. Using deep imaging from 100-500 μm from Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging REceiver (SPIRE) onboard Herschel, we investigate infrared properties of spectroscopic and photo-z cluster members, and of Hα emitters in XMMU J2235.3−2557, one of the most massive, distant, X-ray selected clusters known. Our analysis is based mostly on fitting of the galaxies spectral energy distribution (SED) in the rest-frame 8-1000 μm. We measure total IR luminosity, deriving star formation rates (SFRs) ranging from 89 to 463 M yr−1 for 13 galaxies individually detected by Herschel, all located beyond the core region (r >250 kpc). We perform a stacking analysis of nine star-forming members not detected by PACS, yielding a detection with SFR = 48 ± 16 M yr−1. Using a colour criterion based on a star-forming galaxy SED at the cluster redshift, we select 41 PACS sources as candidate star-forming cluster members. We characterize a population of highly obscured SF galaxies in the outskirts of XMMU J2235.3−2557. We do not find evidence for a reversal of the SF-density relation in this massive, distant cluster.
We use Herschel-PACS far-infrared (IR) data, combined with previous multiband information and mid-IR spectra, to properly account for the presence of an active nucleus and constrain its energetic ...contribution in luminous IR sources at z∼ 2. The sample is composed of 24 sources in the GOODS-South field, with typical IR luminosity of 1012 L⊙. Data from the 4 Ms Chandra X-ray imaging in this field are also used to identify and characterize active galactic nucleus (AGN) emission.
We reproduce the observed spectral energy distribution (SED), decomposed into a host-galaxy and an AGN component. A smooth-torus model for circumnuclear dust is used to account for the direct and reprocessed contribution from the AGN.
We confirm that galaxies with typical
at z∼ 2 are powered predominantly by star formation. An AGN component is present in nine objects (∼35 per cent of the sample) at the 3σ confidence level, but its contribution to the 8-1000
m emission accounts for only ∼5 per cent of the energy budget. The AGN contribution rises to ∼23 per cent over the 5-30
m range (in agreement with Spitzer IRS results) and to ∼60 per cent over the narrow 2-6
m range. The presence of an AGN is confirmed by X-ray data for three (out of nine) sources, with X-ray spectral analysis indicating the presence of significant absorption, i.e. N
H∼ 1023-1024 cm−2. An additional source shows indications of obscured AGN emission from X-ray data. The comparison between the mid-IR-derived X-ray luminosities and those obtained from X-ray data suggests that obscuration is likely present also in the remaining six sources that harbour an AGN according to the SED-fitting analysis.
We combine multi-wavelength data in the AEGIS-XD and C-COSMOS surveys to measure the typical dark matter halo mass of X-ray selected active galactic nuclei (AGN) ... in comparison with far-infrared ...selected star-forming galaxies detected in the Herschel/PEP survey (PACS Evolutionary Probe; ...) and quiescent systems at z ... 1. We develop a novel method to measure the clustering of extragalactic populations that uses photometric redshift probability distribution functions in addition to any spectroscopy. This is advantageous in that all sources in the sample are used in the clustering analysis, not just the subset with secure spectroscopy. The method works best for large samples. The loss of accuracy because of the lack of spectroscopy is balanced by increasing the number of sources used to measure the clustering. We find that X-ray AGN, far-infrared selected star-forming galaxies and passive systems in the redshift interval 0.6 < z < 1.4 are found in haloes of similar mass, ... We argue that this is because the galaxies in all three samples (AGN, star-forming, passive) have similar stellar mass distributions, approximated by the J-band luminosity. Therefore, all galaxies that can potentially host X-ray AGN, because they have stellar masses in the appropriate range, live in dark matter haloes of ... independent of their star formation rates. This suggests that the stellar mass of X-ray AGN hosts is driving the observed clustering properties of this population. We also speculate that trends between AGN properties (e.g. luminosity, level of obscuration) and large-scale environment may be related to differences in the stellar mass of the host galaxies. (ProQuest: ... denotes formulae/symbols omitted.)
Aims. We study the impact of galaxy-galaxy interactions on the far-infrared properties of galaxies and its evolution at 0 < z < 1.2. Methods. Using the high-z galaxies in the fields of Great ...Observatories Origins Deep Survey (GOODS) observed by the Herschel Space Observatory in the framework of the GOODS-Herschel key program and the local IRAS or AKARI-selected galaxies in the field of Sloan Digital Sky Survey Data Release 7, we investigate the dependence of galaxy properties on the morphology of and the distance to the nearest neighbor galaxy. Results. We find that the star-formation rates (SFRs) and the specific SFRs (SSFRs) of galaxies on average depend on the morphology of and the distance to the nearest neighbor galaxy in this redshift range. When a late-type galaxy has a close neighbor galaxy, the SFR and the SSFR increase as it approaches a late-type neighbor, which is supported by Kolmogorov-Smirnov (K-S) and Monte Carlo (MC) tests with a significance level of >99%. However, the SFR and the SSFR decrease or do not change much as the galaxy approaches an early-type neighbor. The bifurcations of SFRs and SSFRs depending on the neighbor’s morphology seem to occur at Rn ≈ 0.5rvir,nei (virial radius of the neighbor), which is supported by K-S and MC tests with a significance level of >98%. For all redshift bins, the SSFRs of late-type galaxies interacting with late-type neighbors are increased by factors of about 1.8 ± 0.7 and 4.0 ± 1.2 compared to those of non-interacting galaxies when the pair separation is smaller than 0.5rvir,nei and 0.1rvir,nei, respectively. The dust temperature of both local and high-z late-type galaxies that strongly interact with late-type neighbors (i.e. Rn ≤ 0.1rvir,nei) appears to be higher than that of non-interacting galaxies with a significance level of 96−99%. However, the dust temperature of local late-type galaxies that strongly interact with early-type neighbors seems to be lower than or similar to that of non-interacting galaxies. Conclusions. Our results suggest that galaxy-galaxy interactions and mergers have been strongly affecting the SFR and the dust properties of star-forming galaxies over at least 8 billion years.
We combine Herschel-Photodetector Array Camera and Spectrometer (PACS) data from the PACS Evolutionary Probe (PEP) program with Spitzer 24 mu m and 16 mu m photometry and ultra deep Infrared ...Spectrograph (IRS) mid-infrared spectra to measure the mid- to far-infrared spectral energy distribution (SED) of 0.7 < z < 2.5 normal star-forming galaxies (SFGs) around the main sequence (the redshift-dependent relation of star formation rate (SFR) and stellar mass). Our very deep data confirm from individual far-infrared detections that z ~ 2 SFRs are overestimated if based on 24 mu m fluxes and SED templates that are calibrated via local trends with luminosity. Galaxies with similar ratios of rest-frame nuL sub(nu)(8) to 8-1000 mu m infrared luminosity (LIR) tend to lie along lines of constant offset from the main sequence. We explore the relation between SED shape and offset in specific star formation rate (SSFR) from the redshift-dependent main sequence. Main-sequence galaxies tend to have a similar nuL sub(nu)(8)/LIR regardless of LIR and redshift, up to z ~ 2.5, and nuL sub(nu)(8)/LIR decreases with increasing offset above the main sequence in a consistent way at the studied redshifts. We provide a redshift-independent calibration of SED templates in the range of 8-60 mu m as a function of Delta log(SSFR) offset from the main sequence. Redshift dependency enters only through the evolution of the main sequence with time. Ultra deep IRS spectra match these SED trends well and verify that they are mostly due to a change in ratio of polycyclic aromatic hydrocarbon (PAH) to LIR rather than continua of hidden active galactic nuclei (AGNs). Alternatively, we discuss the dependence of nuL sub(nu)(8)/LIR on LIR. The same nuL sub(nu)(8)/LIR is reached at increasingly higher LIR at higher redshift, with shifts relative to local by 0.5 and 0.8 dex in log(LIR) at redshifts z ~ 1 and z ~ 2. Corresponding SED template calibrations are provided for use if no stellar masses are on hand. For most of those z ~ 2 SFGs that also host an AGN, the mid-infrared is dominated by the star-forming component.
We use the infrared excess (IRX) FIR/UV luminosity ratio to study the relation between the effective UV attenuation (A sub(IRX)) and the UV spectral slope (beta) in a sample of 450 1 < z < 2.5 ...galaxies. The FIR data are from very deep Herschel observations in the GOODS fields that allow us to detect galaxies with star formation rates (SFRs) typical of galaxies with log(M sub(*))>9.3. Thus, we are able to study galaxies on and even below the main SFR-stellar mass relation (main sequence). We find that main-sequence galaxies form a tight sequence in the IRX-beta plane, which has a flatter slope than commonly used relations. This slope favors a Small-Magellanic-Cloud-like UV extinction curve, though the interpretation is model dependent. The scatter in the A sub(IRX)-beta plane correlates with the position of the galaxies in the SFR-M sub(*) plane. Using a smaller sample of galaxies with CO gas masses, we study the relation between the UV attenuation and the molecular gas content. We find a very tight relation between the scatter in the IRX-beta plane and the specific attenuation S sub(A), a quantity that represents the attenuation contributed by the molecular gas mass per young star. S sub(A) is sensitive to both the geometrical arrangement of stars and dust and to the compactness of the star-forming regions. We use this empirical relation to derive a method for estimating molecular gas masses using only widely available integrated rest-frame UV and FIR photometry. The method produces gas masses with an accuracy between 0.12 and 0.16 dex in samples of normal galaxies between z~0 and z~1.5. Major mergers and submillimeter galaxies follow a different SA relation.
Aims. In this paper we consider a large sample of optically selected clusters, in order to elucidate the physical reasons for the existence of X- ray underluminous clusters. Methods. For this purpose ...we analyzed the correlations of the X-ray and optical properties of a sample of 137 spectroscopically confirmed Abell clusters in the SDSS database. We searched for the X-ray counterpart of each cluster in the ROSAT All Sky Survey. We find that 40% of our clusters have a marginal X-ray detection or remain undetected in X-rays. These clusters appear too X-ray faint on average for their mass as determined by velocity dispersion; i.e. they do not follow the scaling relation between X-ray luminosity and virial mass traced by the other clusters. On the other hand, they do follow the general scaling relation between optical luminosity and virial mass. We refer to these clusters as the X-ray-underluminous Abell clusters (AXU clusters, for short) and designate as "normal" the X-ray detected Abell systems. We separately examined the distributions and properties of the galaxy populations of the normal and the AXU clusters. Results. The AXU clusters are characterized by leptokurtic (more centrally concentrated than a Gaussian) velocity distribution of their member galaxies in the outskirts ( 1.5 < r/r_ \leq 3.5), as expected for the systems in accretion. In addition, the AXU clusters have a higher fraction of blue galaxies in the external region and show a marginally significant paucity of galaxies at the center. Our results seem to support the interpretation that the AXU clusters are systems in formation undergoing a phase of mass accretion. Their low X-ray luminosity should be due to the still accreting intracluster gas or to an ongoing merging process.
ABSTRACT
Based on HST and MUSE data, we probe the stellar and gas properties (i.e. kinematics, stellar mass, star formation rate) of the radio-loud brightest cluster galaxy (BCG) located at the ...centre of the X-ray-luminous cool-core cluster Abell 2667 (z = 0.2343). The bi-dimensional modelling of the BCG surface brightness profile reveals the presence of a complex system of substructures extending all around the galaxy. Clumps of different size and shape plunged into a more diffuse component constitute these substructures, whose intense ‘blue’ optical colour hints at the presence of a young stellar population. Our results depict the BCG as a massive (M⋆ ≃ 1.38 × 1011 M⊙) dispersion-supported spheroid (Δv⋆ ≤ 150 km s−1, σ0 ∼ 216 km s−1) hosting an active supermassive black hole (MSMBH ≃ 3.8 × 109 M⊙) whose optical features are typical of low-ionization nuclear emission line regions. Although the velocity pattern of the stars in the BCG is irregular, the stellar kinematics in the regions of the clumps show a positive velocity of ∼100 km s−1, similarly to the gas component. An analysis of the mechanism giving rise to the observed lines in the clumps through empirical diagnostic diagrams points out that the emission is composite, suggesting contribution from both star formation and an active galactic nucleus. We conclude our analysis describing how scenarios of both chaotic cold accretion and merging with a gas-rich disc galaxy can efficaciously explain the phenomena the BCG is undergoing.
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