We present a study of the infrared properties of X-ray selected, moderate-luminosity (i.e. L
X= 1042-1044 erg s−1) active galactic nuclei (AGNs) up to z ≈ 3, in order to explore the links between ...star formation in galaxies and accretion on to their central black holes. We use 100 and 160 μ m fluxes from GOODS-Herschel - the deepest survey yet undertaken by the Herschel telescope - and show that in the vast majority of cases (i.e. >94 per cent) these fluxes are dominated by emission from the host galaxy. As such, these far-infrared bands provide an uncontaminated view of star formation in the AGN host galaxies. We find no evidence of any correlation between the X-ray and infrared luminosities of moderate AGNs at any redshift, suggesting that global star formation is decoupled from nuclear (i.e. AGN) activity in these galaxies. On the other hand, we confirm that the star formation rates of AGN hosts increase strongly with redshift, by a factor of 43+27
− 18 from z < 0.1 to z = 2-3 for AGNs with the same range of X-ray luminosities. This increase is entirely consistent with the factor of 25-50 increase in the specific star formation rates (SSFRs) of normal, star-forming (i.e. main-sequence) galaxies over the same redshift range. Indeed, the average SSFRs of AGN hosts are only marginally (i.e. ≈20 per cent) lower than those of main-sequence galaxies at all surveyed redshifts, with this small deficit being due to a fraction of AGNs residing in quiescent (i.e. low SSFR) galaxies. We estimate that 79 ± 10 per cent of moderate-luminosity AGNs are hosted in main-sequence galaxies, 15 ± 7 per cent in quiescent galaxies and <10 per cent in strongly starbursting galaxies. We derive the fractions of all main-sequence galaxies at z < 2 that are experiencing a period of moderate nuclear activity, noting that it is strongly dependent on galaxy stellar mass (M
stars), rising from just a few per cent at M
stars∼ 1010 M⊙ to ≳20 per cent at M
stars≥ 1011 M⊙. Our results indicate that it is galaxy stellar mass that is most important in dictating whether a galaxy hosts a moderate-luminosity AGN. We argue that the majority of moderate nuclear activity is fuelled by internal mechanisms rather than violent mergers, which suggests that high-redshift disc instabilities could be an important AGN feeding mechanism.
Two main modes of star formation are know to control the growth of galaxies: a relatively steady one in disk-like galaxies, defining a tight star formation rate (SFR)-stellar mass sequence, and a ...starburst mode in outliers to such a sequence which is generally interpreted as driven by merging. Such starburst galaxies are rare but have much higher SFRs, and it is of interest to establish the relative importance of these two modes. PACS/Herschel observations over the whole COSMOS and GOODS-South fields, in conjunction with previous optical/near-IR data, have allowed us to accurately quantify for the first time the relative contribution of the two modes to the global SFR density in the redshift interval 1.5 < z < 2.5, i.e., at the cosmic peak of the star formation activity. The logarithmic distributions of galaxy SFRs at fixed stellar mass are well described by Gaussians, with starburst galaxies representing only a relatively minor deviation that becomes apparent for SFRs more than four times higher than on the main sequence. Such starburst galaxies represent only 2% of mass-selected star-forming galaxies and account for only 10% of the cosmic SFR density at z ~ 2. Only when limited to SFR > 1000 M yr--1, off-sequence sources significantly contribute to the SFR density (46% ? 20%). We conclude that merger-driven starbursts play a relatively minor role in the formation of stars in galaxies, whereas they may represent a critical phase toward the quenching of star formation and morphological transformation in galaxies.
We use the Sloan Digital Sky Survey (York et al.) data base to explore the effect of the disc inclination angle on the derived star formation rate (SFR), hence on the slope and width of the ...main-sequence (MS) relation for star-forming galaxies. We find that SFRs for nearly edge-on discs are underestimated by factors ranging from ~0.2 dex for low-mass galaxies up to ~0.4 dex for high-mass galaxies. This results in a substantially flatter MS relation for high-inclination discs compared to that for less inclined ones, though the global effect over the whole sample of star-forming galaxies is relatively minor, given the small fraction of high-inclination discs. However, we also find that galaxies with high-inclination discs represent a non-negligible fraction of galaxies populating the so-called green valley, with derived SFRs intermediate between the MS and those of quenched, passively evolving galaxies.
Light breeze in the local Universe Concas, A.; Popesso, P.; Brusa, M. ...
Astronomy & astrophysics,
10/2017, Letnik:
606
Journal Article
Recenzirano
Odprti dostop
We analyze a complete spectroscopic sample of galaxies (~600 000) drawn from Sloan Digital Sky Survey (SDSS, DR7) to look for evidence of galactic winds in the local Universe. We focus on the shape ...of the OIIIλ5007 emission line as a tracer of ionizing gas outflows. We stack our spectra in a fine grid of star formation rate (SFR) and stellar mass to analyze the dependence of winds on the position of galaxies in the SFR versus mass diagram. We do not find any significant evidence of broad and shifted OIIIλ5007 emission line which we interpret as no evidence of outflowing ionized gas in the global population. We have also classified these galaxies as star-forming or AGN-dominated according to their position in the standard BPT diagram. We show how the average OIIIλ5007 profile changes as a function of the nature of the dominant ionizing source. We find that in the star-forming dominated source the oxygen line is symmetric and governed by the gravitational potential well. The AGN or composite AGN\star-formation activity objects, in contrast, display a prominent and asymmetric profile that can be well described by a broad Gaussian component that is blue-shifted from a narrow symmetric core. In particular, we find that the blue wings of the average OIIIλ5007 profiles are increasingly prominent in the LINERs and Seyfert galaxies. We conclude that, through the identification of strong bulk motion as traced by the warm ionized gas, in the low-redshift Universe, “pure” star-formation activity does not seem capable of driving ionized-gas outflows, while, the presence of optically selected AGN seems to play a primary role. We discuss the implications of these results for the role of the quenching mechanism in the present-day Universe.
We study a sample of Herschel selected galaxies within the Great Observatories Origins Deep Survey-South and the Cosmic Evolution Survey fields in the framework of the Photodetector Array Camera and ...Spectrometer (PACS) Evolutionary Probe project. Starting from the rich multiwavelength photometric data sets available in both fields, we perform a broad-band spectral energy distribution decomposition to disentangle the possible active galactic nucleus (AGN) contribution from that related to the host galaxy. We find that 37 per cent of the Herschel-selected sample shows signatures of nuclear activity at the 99 per cent confidence level. The probability of revealing AGN activity increases for bright (L
1−1000 > 1011
L
) star-forming galaxies at z > 0.3, becoming about 80 per cent for the brightest (L
1−1000 > 1012
L
) infrared (IR) galaxies at z ≥ 1. Finally, we reconstruct the AGN bolometric luminosity function and the supermassive black hole growth rate across cosmic time up to z ∼ 3 from a far-IR perspective. This work shows general agreement with most of the panchromatic estimates from the literature, with the global black hole growth peaking at z ∼ 2 and reproducing the observed local black hole mass density with consistent values of the radiative efficiency rad (∼0.07).
Context.Some previous investigations have found that the fraction (fAGN) of active galactic nuclei (AGNs) is lower in clusters than in the field. This can result from the suppression of galaxy–galaxy ...mergers in high-velocity dispersion ($\sigma_v$) clusters, if the formation and/or fueling of AGNs is directly related to the merging process. Aims.We investigate the existence of a relation between fAGN and $\sigma_v$ in galaxy clusters in order to shed light on the formation and evolution processes of AGNs and cluster galaxies. Methods.Using data from the Sloan Digital Sky Survey we determine fAGN and $\sigma_v$ for the clusters in two samples, extracted from the catalogs of Popesso et al. (2006a, A&A, in press) and Miller et al. (2005, AJ, 130, 968), and excluding clusters with significant evidence for substructures. Results.We find a significant $f_{\rm AGN}{-}\sigma_v$ anti-correlation. Clusters with $\sigma_v$ lower and, respectively, higher than 500 km s-1 have AGN fractions of $0.21 \pm 0.01$ and $0.15 \pm 0.01$, on average. The $f_{\rm AGN}{-}\sigma_v$ relation can be described by a model that assumes fAGN is proportional to the galaxies merging rate, plus a constant. Conclusions.Since fAGN increases with decreasing $\sigma_v$, AGNs are likely to have played a significant rôle in heating the intra-cluster medium and driving galaxy evolution in cluster precursors and groups.
We present the clustering properties of a complete sample of 968 radio sources detected at 1.4 GHz by the Very Large Array (VLA)-COSMOS survey with radio fluxes brighter than 0.15 mJy. 92 per cent ...have redshift determinations from the Laigle et al. catalogue. Based on their radio luminosity, these objects have been divided into 644 AGN and 247 star-forming galaxies. By fixing the slope of the autocorrelation function to ... = 2, we find r sub( 0)=11.7... Mpc for the clustering length of the whole sample, while r sub( 0)=11.2... Mpc and r sub( 0)=7.8... Mpc (r sub( 0)=6.8... Mpc for z less than or equal to 0.9) are, respectively, obtained for AGN and star-forming galaxies. These values correspond to minimum masses for dark matter haloes of M sub( min)=10... M... for radio-selected AGN and M sub( min)=10... M... for radio-emitting star-forming galaxies (M sub( min)=10... M... for z less than or equal to 0.9). Comparisons with previous works imply an independence of the clustering properties of the AGN population with respect to both radio luminosity and redshift. We also investigate the relationship between dark and luminous matter in both populations. We obtain ...M*.../M sub( halo) ... 10 super( - 2.7) for AGN, and ...M*.../M sub( halo) ... 10 super( - 2.4) in the case of star-forming galaxies. Furthermore, if we restrict to z ... 0.9 star-forming galaxies, we derive ...M*.../M sub( halo) ... 10 super( - 2.1), result that clearly shows the cosmic process of stellar build-up as one moves towards the more local universe. Comparisons between the observed space density of radio-selected AGN and that of dark matter haloes show that about one in two haloes is associated with a black hole in its radio-active phase. This suggests that the radio-active phase is a recurrent phenomenon. (ProQuest: ... denotes formulae/symbols omitted.)
We present results from the deepest Herschel-Photodetector Array Camera and Spectrometer (PACS) far-infrared blank field extragalactic survey, obtained by combining observations of the Great ...Observatories Origins Deep Survey (GOODS) fields from the PACS Evolutionary Probe (PEP) and GOODS-Herschel key programmes. We describe data reduction and theconstruction of images and catalogues. In the deepest parts of the GOODS-S field, the catalogues reach 3σ depths of 0.9, 0.6 and 1.3 mJy at 70, 100 and 160 μm, respectively, and resolve ~75% of the cosmic infrared background at 100 μm and 160 μm into individually detected sources. We use these data to estimate the PACS confusion noise, to derive the PACS number counts down to unprecedented depths, and to determine the infrared luminosity function of galaxies down to LIR = 1011 L⊙ at z ~ 1 and LIR = 1012 L⊙ at z ~ 2, respectively. For the infrared luminosity function of galaxies, our deep Herschel far-infrared observations are fundamental because they provide more accurate infrared luminosity estimates than those previously obtained from mid-infrared observations. Maps and source catalogues (>3σ) are now publicly released. Combined with the large wealth of multi-wavelength data available for the GOODS fields, these data provide a powerful new tool for studying galaxy evolution over a broad range of redshifts.
We use deep Herschel observations taken with both PACS and SPIRE imaging cameras to estimate the dust mass of a sample of galaxies extracted from the GOODS-S, GOODS-N and the COSMOS fields. We divide ...the redshift–stellar mass (Mstar)–star formation rate (SFR) parameter space into small bins and investigate average properties over this grid. In the first part of the work we investigate the scaling relations between dust mass, stellar mass and SFR out to z = 2.5. No clear evolution of the dust mass with redshift is observed at a given SFR and stellar mass. We find a tight correlation between the SFR and the dust mass, which, under reasonableassumptions, is likely a consequence of the Schmidt-Kennicutt (S-K) relation. The previously observed correlation between the stellar content and the dust content flattens or sometimes disappears when considering galaxies with the same SFR. Our finding suggests that most of the correlation between dust mass and stellar mass obtained by previous studies is likely a consequence of the correlation between the dust mass and the SFR combined with the main sequence, i.e., the tight relation observed between the stellar mass and the SFR and followed by the majority of star-forming galaxies. We then investigate the gas content as inferred from dust mass measurements. We convert the dust mass into gas mass by assuming that the dust-to-gas ratio scales linearly with the gas metallicity (as supported by many observations). For normal star-forming galaxies (on the main sequence) the inferred relation between the SFR and the gas mass (integrated S-K relation) broadly agrees with the results of previous studies based on CO measurements, despite the completely different approaches. We observe that all galaxies in the sample follow, within uncertainties, the same S-K relation. However, when investigated in redshift intervals, the S-K relation shows a moderate, but significant redshift evolution. The bulk of the galaxy population at z ~ 2 converts gas into stars with an efficiency (star formation efficiency, SFE = SFR/Mgas, equal to the inverse of the depletion time) about 5 times higher than at z ~ 0. However, it is not clear what fraction of such variation of the SFE is due to an intrinsic redshift evolution and what fraction is simply a consequence of high-z galaxies having, on average, higher SFR, combined with the super-linear slope of the S-K relation (while other studies find a linear slope). We confirm that the gas fraction (fgas = Mgas/(Mgas + Mstar)) decreases with stellar mass and increases with the SFR. We observe no evolution with redshift once Mstarand SFR are fixed. We explain these trends by introducing a universal relation between gas fraction, stellar mass and SFR that does not evolve with redshift, at least out to z ~ 2.5. Galaxies move across this relation as their gas content evolves across the cosmic epochs. We use the 3D fundamental fgas–Mstar–SFR relation, along with the evolution of the main sequence with redshift, to estimate the evolution of the gas fraction in the average population of galaxies as a function of redshift and as a function of stellar mass: we find that Mstar ≳ 1011 M⊙ galaxies show the strongest evolution at z ≳ 1.3 and a flatter trend at lower redshift, while fgas decreases more regularly over the entire redshift range probed in Mstar ≲ 1011 M⊙ galaxies, in agreement with a downsizing scenario.
ABSTRACT
We use dust masses (Mdust) derived from far-infrared data and molecular gas masses (Mmol) based on CO luminosity to calibrate proxies based on a combination of the galaxy Balmer decrement, ...disc inclination, and gas metallicity. We use such proxies to estimate Mdust and Mmol in the local SDSS sample of star-forming galaxies (SFGs). We study the distribution of Mdust and Mmol along and across the main sequence (MS) of SFGs. We find that Mdust and Mmol increase rapidly along the MS with increasing stellar mass (M*), and more marginally across the MS with increasing SFR (or distance from the relation). The dependence on M* is sub-linear for both Mdust and Mmol. Thus, the fraction of dust (fdust) and molecular gas mass (fmol) decreases monotonically towards large M*. The star formation efficiency (SFE, inverse of the molecular gas depletion time) depends strongly on the distance from the MS and it is constant along the MS. As nearly all galaxies in the sample are central galaxies, we estimate the dependence of fdust and fgas on the host halo mass and find a tight anticorrelation. As the region where the MS is bending is numerically dominated by massive haloes, we conclude that the bending of the MS is due to a lower availability of molecular gas mass in massive haloes rather than a lower efficiency in forming stars.
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