F. Pozzi

University of Bologna, Bolonia, Emilia-Romagna, Italy

Are you F. Pozzi?

Claim your profile

Publications (176)592.79 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Using data from four deep fields (COSMOS, AEGIS, ECDFS, and CDFN), we study the correlation between the position of galaxies in the star formation rate (SFR) versus stellar mass plane and local environment at z < 1.1. To accurately estimate the galaxy SFR, we use the deepest available Spitzer/MIPS 24 and Herschel/PACS data sets. We distinguish group environments (Mhalo ∼ 1012.5–14.2 M⊙) based on the available deep X-ray data and lower halo mass environments based on the local galaxy density. We confirm that the main sequence (MS) of star-forming galaxies is not a linear relation and there is a flattening towards higher stellar masses (M* > 1010.4–10.6 M⊙), across all environments. At high redshift (0.5 < z < 1.1), the MS varies little with environment. At low redshift (0.15 < z < 0.5), group galaxies tend to deviate from the mean MS towards the region of quiescence with respect to isolated galaxies and less-dense environments. We find that the flattening of the MS towards low SFR is due to an increased fraction of bulge-dominated galaxies at high masses. Instead, the deviation of group galaxies from the MS at low redshift is caused by a large fraction of red disc-dominated galaxies which are not present in the lower density environments. Our results suggest that above a mass threshold (∼1010.4–1010.6 M⊙) stellar mass, morphology and environment act together in driving the evolution of the star formation activity towards lower level. The presence of a dominating bulge and the associated quenching processes are already in place beyond z ∼1. The environmental effects appear, instead, at lower redshifts and have a long time-scale.
    Full-text · Article · Dec 2015 · Monthly Notices of the Royal Astronomical Society
  • [Show abstract] [Hide abstract]
    ABSTRACT: In order to investigate the far-infrared (FIR) properties of radio-active active galactic nuclei (AGN), we have considered three different fields where both radio and FIR observations are the deepest to date: GOODS-South, GOODS-North and the Lockman Hole. Out of a total of 92 radio-selected AGN, ∼64 per cent are found to have a counterpart in Herschel maps. The percentage is maximum in the GOODS-North (72 per cent) and minimum (∼50 per cent) in the Lockman Hole, where FIR observations are shallower. Our study shows that in all cases FIR emission is associated with star-forming activity within the host galaxy. Such an activity can even be extremely intense, with star-forming rates as high as ∼103–104 M⊙ yr−1. AGN activity does not inhibit star formation in the host galaxy, just as on-site star formation does not seem to affect AGN properties, at least those detected at radio wavelengths and for z ≳ 1. Given the very high rate of FIR detections, we stress that this refers to the majority of the sample: most radio-active AGN are associated with intense episodes of star formation. However, the two processes proceed independently within the same galaxy, at all redshifts but in the local universe, where powerful enough radio activity reaches the necessary strength to switch off the on-site star formation. Our data also show that for z ≳ 1 the hosts of radio-selected star-forming galaxies and AGN are indistinguishable from each other in terms of both mass and IR luminosity distributions. The two populations only differentiate in the very local universe, whereby the few AGN which are still FIR-active are found in galaxies with much higher masses and luminosities.
    No preview · Article · Nov 2015 · Monthly Notices of the Royal Astronomical Society
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We derive the carbon monoxide (CO) luminosity function (LF) for different rotational transitions [i.e. (1–0), (3–2), (5–4)] starting from the Herschel LF by Gruppioni et al. and using appropriate LCO–LIR conversions for different galaxy classes. Our predicted LFs fit the data so far available at z ≈ 0 and 2. We compare our results with those obtained by semi-analytical models (SAMs): while we find a good agreement over the whole range of luminosities at z ≈ 0, at z ≈ 1 and z ≈ 2, the tension between our LFs and SAMs in the faint and bright ends increases. We finally discuss the contribution of luminous active galactic nucleus (LX > 1044 erg s− 1) to the bright end of the CO LF concluding that they are too rare to reproduce the actual CO LF at z ≈ 2.
    Preview · Article · Nov 2015 · Monthly Notices of the Royal Astronomical Society Letters
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We use a spectroscopic sample of 286 star-forming galaxies (SFGs) at 1<z<3 from the GMASS survey to study different star formation rate (SFR) estimators. Infrared (IR) data are used to derive empirical calibrations to correct ultraviolet (UV) and [OII]{\lambda}3727 luminosities for dust extinction and dust-corrected estimates of SFR. In the selection procedure we fully exploit the available spectroscopic information. On the basis of three continuum indices, we are able to identify and exclude from the sample galaxies in which old stellar populations might bring a non-negligible contribution to IR luminosity (LIR) and continuum reddening. Using Spitzer-MIPS and Herschel-PACS data we derive LIR for two-thirds of our sample. The LIR/LUV ratio is used as a probe of effective attenuation (AIRX) to search for correlations with continuum and spectroscopic features. The relation between AIRX and UV continuum slope ({\beta}) was tested for our sample and found to be broadly consistent with the literature results at the same redshift, though with a larger dispersion with respect to UV-selected samples. We find a correlation between the rest-frame equivalent width (EW) of the [OII]{\lambda}3727 line and {\beta}, which is the main result of this work. We therefore propose the [OII]{\lambda}3727 line EW as a dust attenuation probe and calibrate it through AIRX, though the assumption of a reddening curve is still needed to derive the actual attenuation towards the [OII]{\lambda}3727 line. We tested the issue of differential attenuation towards stellar continuum and nebular emission: our results are in line with the traditional prescription of extra attenuation towards nebular lines. A set of relations is provided that allows the recovery of the total unattenuated SFR from UV and [OII]{\lambda}3727 luminosities. (Abridged)
    Full-text · Article · Aug 2015 · Astronomy and Astrophysics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present predictions for number counts and redshift distributions of galaxies detectable in continuum and in emission lines with the Mid-infrared (MIR) Instrument (SMI) proposed for the Space Infrared Telescope for Cosmology and Astrophysics. We have considered 24 MIR fine-structure lines, four polycyclic aromatic hydrocarbon bands (at 6.2, 7.7, 8.6 and 11.3 μm) and two silicate bands (in emission and in absorption) at 9.7 and 18.0 μm. Six of these lines are primarily associated with active galactic nuclei (AGNs), the others with star formation. A survey with the SMI spectrometers of 1-h integration per field of view (FoV) over an area of 1 deg2 will yield 5σ detections of ≃ 140 AGN lines and of ≃ 5.2 × 104 star-forming galaxies, ≃ 1.6 × 104 of which will be detected in at least two lines. The combination of a shallow (20.0 deg2, 1.4 × 10−1 h integration per FoV) and a deep survey (6.9 × 10−3 deg2, 635 h integration time), with the SMI camera, for a total of ∼1000 h, will accurately determine the MIR number counts of galaxies and of AGNs over five orders of magnitude in flux density, reaching values more than one order of magnitude fainter than the deepest Spitzer 24 μm surveys. This will allow us to determine the cosmic star formation rate (SFR) function down to SFRs more than 100 times fainter than reached by the Herschel Observatory.
    Full-text · Article · Jun 2015 · Monthly Notices of the Royal Astronomical Society
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present a direct comparison between the observed star formation rate functions (SFRFs) and the state-of-the-art predictions of semi-analytic models (SAMs) of galaxy formation and evolution. We use the PACS Evolutionary Probe Survey and Herschel Multi-tiered Extragalactic Survey data sets in the COSMOS and GOODS-South fields, combined with broad-band photometry from UV to sub-mm, to obtain total (IR+UV) instantaneous star formation rates (SFRs) for individual Herschel galaxies up to z ∼ 4, subtracted of possible active galactic nucleus (AGN) contamination. The comparison with model predictions shows that SAMs broadly reproduce the observed SFRFs up to z ∼ 2, when the observational errors on the SFR are taken into account. However, all the models seem to underpredict the bright end of the SFRF at z ≳ 2. The cause of this underprediction could lie in an improper modelling of several model ingredients, like too strong (AGN or stellar) feedback in the brighter objects or too low fallback of gas, caused by weak feedback and outflows at earlier epochs.
    No preview · Article · Jun 2015 · Monthly Notices of the Royal Astronomical Society
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Highly obscured active galactic nuclei (AGN) are common in nearby galaxies, but are difficult to observe beyond the local Universe, where they are expected to significantly contribute to the black hole accretion rate density. Furthermore, Compton-thick (CT) absorbers (NH>10^24 cm^-2) suppress even the hard X-ray (2-10 keV) AGN nuclear emission, and therefore the column density distribution above 10^24 cm^-2 is largely unknown. We present the identification and multi-wavelength properties of a heavily obscured (NH>~10^25 cm^-2), intrinsically luminous (L(2-10keV)>10^44 erg s^-1) AGN at z=0.353 in the COSMOS field. Several independent indicators, such as the shape of the X-ray spectrum, the decomposition of the spectral energy distribution and X-ray/[NeV] and X-ray/6{\mu}m luminosity ratios, agree on the fact that the nuclear emission must be suppressed by a 10^25 cm^-2 column density. The host galaxy properties show that this highly obscured AGN is hosted in a massive star-forming galaxy, showing a barred morphology, which is known to correlate with the presence of CT absorbers. Finally, asymmetric and blueshifted components in several optical high-ionization emission lines indicate the presence of a galactic outflow, possibly driven by the intense AGN activity (L(Bol)/L(Edd) = 0.3-0.5). Such highly obscured, highly accreting AGN are intrinsically very rare at low redshift, whereas they are expected to be much more common at the peak of the star formation and BH accretion history, at z~2-3. We demonstrate that a fully multi-wavelength approach can recover a sizable sample of such peculiar sources in large and deep surveys such as COSMOS.
    Full-text · Article · May 2015 · Astronomy and Astrophysics
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present a backward approach for the interpretation of the evolution of the near-IR and the far-IR luminosity functions (LFs) across the redshift range 0 < z < 3. In our method, late-type galaxies are treated by means of a parametric phenomenological method based on PEP/HerMES data up to z ∼ 4, whereas spheroids are described by means of a physically motivated backward model. The spectral evolution of spheroids is modeled by means of a single-mass model, associated with a present-day elliptical with a K-band luminosity comparable to the break of the local early-type LF. The formation of proto-spheroids is assumed to occurr across the redshift range 1 ≤ z ≤ 5. The key parameter is represented by the redshift z0.5 at which half of all proto-spheroids are already formed. For this parameter, a statistical study indicates values between z0.5 = 1.5 and z0.5 = 3. We assume z0.5 ∼ 2 as the fiducial value and show that this assumption allows us to describe accourately the redshift distributions and the source counts. By assuming z0.5 ∼ 2 at the far-IR flux limit of the PEP-COSMOS survey, the PEP-selected sources observed at z> 2 can be explained as progenitors of local spheroids caught during their formation. We also test the effects of mass downsizing by dividing the spheroids into three populations of different present-day stellar masses. The results obtained in this case confirm the validity of our approach, i.e., that the bulk of proto-spheroids can be modeled by means of a single model that describes the evolution of galaxies at the break of the present-day early-type K-band LF. © 2015. The American Astronomical Society. All rights reserved.
    No preview · Article · Apr 2015 · The Astrophysical Journal
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a backward approach for the interpretation of the evolution of the near-infrared and the far-infrared luminosity functions across the redshift range 0<z<3. In our method, late-type galaxies are treated by means of a parametric phenomenological method based on PEP/HerMES data up to z~4, whereas spheroids are described by means of a physically motivated backward model. The spectral evolution of spheroids is modelled by means of a single-mass model, associated to a present-day elliptical with K-band luminosity comparable to the break of the local early-type luminosity function. The formation of proto-spheroids is assumed to occurr across the redshift range 1< z < 5. The key parameter is represented by the redshift z_0.5 at which half proto-spheroids are already formed. A statistical study indicates for this parameter values between z_0.5=1.5 and z_0.5=3. We assume as fiducial value z_0.5~2, and show that this assumption allows us to describe accourately the redshift distributions and the source counts. By assuming z_0.5 ~ 2 at the far-IR flux limit of the PEP-COSMOS survey, the PEP-selected sources observed at z>2 can be explained as progenitors of local spheroids caught during their formation. We also test the effects of mass downsizing by dividing the spheroids into three populations of different present-day stellar masses. The results obtained in this case confirm the validity of our approach, i.e. that the bulk of proto-spheroids can be modelled by means of a single model which describes the evolution of galaxies at the break of the present-day early type K-band LF.
    Full-text · Article · Feb 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We study the relation of AGN accretion, star formation rate (SFR) and stellar mass (M*) using a sample of ≈8600 star-forming galaxies up to z = 2.5 selected with Herschel imaging in the GOODS and COSMOS fields. For each of them we derive SFR and M*, both corrected, when necessary, for emission from an active galactic nucleus (AGN), through the decomposition of their spectral energy distributions (SEDs). About 10 per cent of the sample are detected individually in Chandra observations of the fields. For the rest of the sample, we stack the X-ray maps to get average X-ray properties. After subtracting the X-ray luminosity expected from star formation and correcting for nuclear obscuration, we derive the average AGN accretion rate for both detected sources and stacks, as a function of M*, SFR and redshift. The average accretion rate correlates with SFR and with M*. The dependence on SFR becomes progressively more significant at z > 0.8. This may suggest that SFR is the original driver of these correlations. We find that average AGN accretion and star formation increase in a similar fashion with offset from the star-forming ‘main-sequence’. Our interpretation is that accretion on to the central black hole and star formation broadly trace each other, irrespective of whether the galaxy is evolving steadily on the main-sequence or bursting.
    Full-text · Article · Jan 2015 · Monthly Notices of the Royal Astronomical Society
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the co-evolution of black-hole-accretion-rate (BHAR) and star-formation-rate (SFR) in $1.5<z<2.5$ galaxies displaying a greater diversity of star-forming properties compared to previous studies. We combine X-ray stacking and far-IR photometry of stellar mass-limited samples of normal star-forming, starburst and quiescent/quenched galaxies in the COSMOS field. We corroborate the existence of a strong correlation between BHAR (i.e. the X-ray luminosity, L_X), and stellar mass (M*) for normal star-forming galaxies, although find a steeper relation than previously reported. We find that starbursts show a factor of 3 enhancement in BHAR compared to normal SF galaxies (against a factor of 6 excess in SFR), while quiescents show a deficit of a factor 5.5 at a given mass. One possible interpretation of this is that the starburst phase does not coincide with cosmologically relevant BH growth, or that starburst-inducing mergers are more efficient at boosting SFR than BHAR. Contrary to studies based on smaller samples, we find the BHAR/SFR ratio of main sequence (MS) galaxies is not mass invariant, but scales weakly as M*^(0.43\pm0.09}, implying faster BH growth in more massive galaxies at $z\sim2$. Furthermore, BHAR/SFR during the starburst is a factor of 2 lower than in MS galaxies, at odds with the predictions of hydrodynamical simulations of merger galaxies that foresee a sudden enhancement of L_X/SFR during the merger. Finally, we estimate that the bulk of the accretion density of the Universe at $z\sim2$ is associated with normal star-forming systems, with only 6(+/-1)% and 11(+/-1)% associated with starburst and quiescent galaxies, respectively.
    Full-text · Article · Jan 2015 · The Astrophysical Journal Letters
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: [Abridged] We study the evolution of the radio spectral index and far-infrared/radio correlation (FRC) across the star-formation rate-stellar masse (i.e. SFR-M*) plane up to z 2. We start from a M*-selected sample of galaxies with reliable SFR and redshift estimates. We then grid the SFR-M* plane in several redshift ranges and measure the infrared luminosity, radio luminosity, radio spectral index, and ultimately the FRC index (i.e. qFIR) of each SFR-M*-z bin. The infrared luminosities of our SFR-M*-z bins are estimated using their stacked far-infrared flux densities inferred from observations obtained with Herschel. Their radio luminosities and radio spectral indices (i.e. alpha, where Snu nu^-alpha) are estimated using their stacked 1.4GHz and 610MHz flux densities from the VLA and GMRT, respectively. Our far-infrared and radio observations include the most widely studied blank extragalactic fields -GOODS-N/S, ECDFS, and COSMOS- covering a sky area of 2deg^2. Using this methodology, we constrain the radio spectral index and FRC index of star-forming galaxies with M*>10^10Msun and 0<z<2.3. We find that alpha^1.4GHz_610MHz does not evolve significantly with redshift or with the distance of a galaxy with respect to the main sequence (MS) of the SFR-M* plane (i.e. Delta_log(SSFR)_MS=log[SSFR(galaxy)/SSFR_MS(M*,z)]). Instead, star-forming galaxies have a radio spectral index consistent with a canonical value of 0.8, which suggests that their radio spectra are dominated by non-thermal optically thin synchrotron emission. We find that qFIR displays a moderate but statistically significant redshift evolution as qFIR(z)=(2.35+/-0.08)*(1+z)^(-0.12+/-0.04), consistent with some previous literature. Finally, we find no significant correlation between qFIR and Delta_log(SSFR)_MS, though a weak positive trend, as observed in one of our redshift bins, cannot be firmly ruled out using our dataset.
    Full-text · Article · Oct 2014 · Astronomy and Astrophysics
  • Source

    Full-text · Conference Paper · Sep 2014
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We study the evolution of the total star formation (SF) activity, total stellar mass (ΣM*) and halo occupation distribution (HOD) in massive haloes by using one of the largest X-ray selected sample of galaxy groups with secure spectroscopic identification in the major blank field surveys (ECDFS, CDFN, COSMOS, AEGIS). We provide an accurate measurement of star formation rate (SFR) for the bulk of the star-forming galaxies using very deep mid-infrared Spitzer MIPS and far-infrared Herschel PACS observations. For undetected IR sources, we provide a well-calibrated SFR from spectral energy distribution (SED) fitting. We observe a clear evolution in the level of SF activity in galaxy groups. The total SF activity in the high-redshift groups (0.5 < z < 1.1) is higher with respect to the low-redshift (0.15 < z < 0.5) sample at any mass by 0.8 ± 0.12 dex. A milder difference (0.35 ± 0.1 dex) is observed between the low-redshift bin and the groups at z ∼ 0. We show that the level of SF activity is declining more rapidly in the more massive haloes than in the more common lower mass haloes. We do not observe any evolution in the HOD and total stellar mass–halo mass relations in groups. The picture emerging from our findings suggests that the galaxy population in the most massive systems is evolving faster than galaxies in lower mass haloes, consistently with a ‘halo downsizing’ scenario.
    Full-text · Article · Sep 2014 · Monthly Notices of the Royal Astronomical Society
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Heavily obscured, Compton Thick (CT, NH>10^24 cm-2) AGN may represent an important phase in AGN/galaxy co-evolution and are expected to provide a significant contribution to the cosmic X-ray background (CXB) at its peak. Through direct X-ray spectra analysis, we selected 39 heavily obscured AGN (NH>3x10^23 cm-2) in the 2 deg^2 XMM-COSMOS survey. Thanks to deeper Chandra data available in the field, we can define 10 of these sources as bona-fide CT, spanning a large range of redshift and luminosity, and estimate the efficiency of our selection to be of the order of 80%. We collected the multi-wavelength information available for these sources, to study the distribution of BH mass (MBH), Eddington ratio (lambda_Edd), stellar mass (M*), specific star formation rate (sSFR) in comparison with a sample of unobscured AGN. We find that highly obscured sources tend to have significantly smaller MBH and higher lambda_Edd with respect to unobscured sources. The sSFR of highly obscured sources is consistent with the one observed for main sequence star forming galaxies, at all redshift. We also present and briefly discuss optical spectra, broad band spectral energy distribution (SED) and morphology for the sample of 10 CT AGN. Both the optical spectra and SED agree with the classification as highly obscured sources: all the available optical spectra are dominated by the stellar component of the host galaxy, and an highly obscured torus component is needed in the SED of all the CT sources. Exploiting the high resolution Hubble images, we show that these highly obscured sources have a significantly larger merger fraction with respect to other X-ray selected samples of AGN. Finally we discuss the implications of our findings in the context of AGN/galaxy co-evolutionary models, and compare our results with the predictions of CXB synthesis models.
    Full-text · Article · Sep 2014 · Astronomy and Astrophysics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present new estimates of redshift-dependent luminosity functions of IR lines detectable by SPICA/SAFARI and excited both by star formation and by AGN activity. The new estimates improve over previous work by using updated evolutionary models and dealing in a self consistent way with emission of galaxies as a whole, including both the starburst and the AGN component. New relationships between line and AGN bolometric luminosity have been derived and those between line and IR luminosities of the starburst component have been updated. These ingredients were used to work out predictions for the source counts in 11 mid/far-IR emission lines partially or entirely excited by AGN activity. We find that the statistics of the emission line detection of galaxies as a whole is mainly determined by the star formation rate, because of the rarity of bright AGNs. We also find that the slope of the line integral number counts is flatter than 2 implying that the number of detections at fixed observing time increases more by extending the survey area than by going deeper. We thus propose a wide spectroscopic survey of 1 hour integration per field-of-view over an area of 5 deg$^{2}$ to detect (at 5${\sigma}$) ~760 AGNs in [OIV]25.89${\mu}$m - the brightest AGN mid-infrared line - out to z~2. Pointed observations of strongly lensed or hyper-luminous galaxies previously detected by large area surveys such as those by Herschel and by the SPT can provide key information on the galaxy-AGN co-evolution out to higher redshifts.
    Full-text · Article · Aug 2014 · Monthly Notices of the Royal Astronomical Society
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Full-text · Article · Jul 2014 · Astronomy and Astrophysics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Context. The most striking feature of the cosmic star formation history (CSFH) of the Universe is a dramatic drop in the star formation (SF) activity after z ~ 1. Aims. In this work we investigate whether the very same process of assembly and growth of structures is one of the major drivers of the observed decline in the Universe’s SF activity. Methods. We study the contribution to the CSFH of galaxies in halos of different masses. This is done by studying the total SF rate-halo mass-redshift plane from redshift 0 to redshift ~1.6 in a sample of 57 groups and clusters by using the deepest available mid- and far-infrared surveys conducted with Spitzer MIPS and Herschel PACS and SPIRE, on blank (ECDFS, CDFN, and the COSMOS) and cluster fields. Results. Our results show that low mass groups (M_(halo) ~ 6 × 10^(12)−6 × 10^(13) M_⊙) provide a 60−80% contribution to the CSFH at z ~ 1. This contribution has declined faster than the CSFH in the past 8 billion years to less than 10% at z 6 × 10^(13) M_⊙) provide only a marginal contribution (50%) of very massive, highly star-forming main sequence galaxies. Below z ~ 1 a quenching process must take place in massive halos to cause the observed faster suppression of their SF activity. Such a process must be a slow one, though, since most of the models implementing a rapid quenching of the SF activity in accreting satellites significantly underpredict the observed SF level in massive halos at any redshift. This would rule out short time-scale mechanisms such as ram pressure stripping. Instead, starvation or the satellite’s transition from cold to hot accretion would provide a quenching timescale of 1 to few Gyr that is more consistent with the observations. Conclusions. Our results suggest a scenario in which, owing to the structure formation process, more and more galaxies experience the group environment and the associated quenching process in the past 8 billion years. This leads to the progressive suppression of their SF activity so that it shapes the CSFH below z ~ 1.
    Full-text · Article · Jul 2014
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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) [LX(2–10 keV) > 1042 erg s− 1] in comparison with far-infrared selected star-forming galaxies detected in the Herschel/PEP survey (PACS Evolutionary Probe; LIR > 1011 L⊙) 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, log MDMH/(M⊙ h−1) ≈ 13.0. 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 log MDMH/(M⊙ h−1) ≈ 13.0 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.
    Full-text · Article · Jul 2014 · Monthly Notices of the Royal Astronomical Society
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We compare various star formation rate (SFR) indicators for star-forming galaxies at 1.4 < z < 2.5 in the COSMOS field. The main focus is on the SFRs from the far-IR (PACS-Herschel data) with those from the ultraviolet, for galaxies selected according to the BzK criterion. FIR-selected samples lead to a vastly different slope of the SFR–stellar mass (M*) relation, compared to that of the dominant main-sequence population as measured from the UV, since the FIR selection picks predominantly only a minority of outliers. However, there is overall agreement between the main sequences derived with the two SFR indicators, when stacking on the PACS maps the BzK-selected galaxies. The resulting logarithmic slope of the SFR–M* relation is ∼0.8–0.9, in agreement with that derived from the dust-corrected UV luminosity. Exploiting deeper 24 μm Spitzer data, we have characterized a subsample of galaxies with reddening and SFRs poorly constrained, as they are very faint in the B band. The combination of Herschel with Spitzer data has allowed us to largely break the age/reddening degeneracy for these intriguing sources, by distinguishing whether a galaxy is very red in B-z because of being heavily dust reddened, or whether because star formation has been (or is being) quenched. Finally, we have compared our SFR(UV) to the SFRs derived by stacking the radio data and to those derived from the Hα luminosity of a sample of star-forming galaxies at 1.4 < z < 1.7. The two sets of SFRs are broadly consistent as they are with the SFRs derived from the UV and by stacking the corresponding PACS data in various mass bins.
    Full-text · Article · Jun 2014 · Monthly Notices of the Royal Astronomical Society

Publication Stats

4k Citations
592.79 Total Impact Points

Institutions

  • 2000-2015
    • University of Bologna
      • Department of Physics and Astronomy DIFA
      Bolonia, Emilia-Romagna, Italy
  • 2012
    • The University of Edinburgh
      • Institute for Astronomy (IfA)
      Edinburgh, Scotland, United Kingdom
    • University of Pavia
      Ticinum, Lombardy, Italy
    • Paris Diderot University
      Lutetia Parisorum, Île-de-France, France
  • 2007-2012
    • Università degli Studi di Siena
      Siena, Tuscany, Italy
  • 2004-2012
    • University of Sussex
      • Astronomy Centre
      Brighton, England, United Kingdom
  • 2001-2012
    • The Astronomical Observatory of Brera
      Merate, Lombardy, Italy
  • 2011
    • Universidad de La Laguna
      • Department of Astrophysics
      San Cristóbal de La Laguna, Canary Islands, Spain
  • 2008
    • National Institute of Astrophysics
      Roma, Latium, Italy