We study the star formation quenching mechanism in cluster galaxies by fitting the spectral energy distribution (SED) of the Herschel Reference Survey, a complete volume-limited K-band-selected ...sample of nearby galaxies including objects in different density regions, from the core of the Virgo cluster to the general field. The SEDs of the target galaxies were fitted using the CIGALE SED modelling code. The truncated activity of cluster galaxies was parametrised using a specific star formation history with two free parameters, the quenching age QA and the quenching factor QF. These two parameters are crucial for the identification of the quenching mechanism, which acts on long timescales when starvation processes are at work, but is rapid and efficient when ram pressure occurs. To be sensitive to an abrupt and recent variation of the star formation activity, we combined twenty photometric bands in the UV to far-infrared in a new way with three age-sensitive Balmer line absorption indices extracted from available medium-resolution (R ~ 1000) integrated spectroscopy and with Hα narrow-band imaging data. The use of a truncated star formation history significantly increases the quality of the fit in HI-deficient galaxies of the sample, that is to say, in those objects whose atomic gas content has been removed during the interaction with the hostile cluster environment. The typical quenching age of the perturbed late-type galaxies is QA ≲ 300 Myr whenever the activity of star formation is reduced by 50% < QF ≤ 80% and QA ≲ 500 Myr for QF > 80%, while that of the quiescent early-type objects is QA ≃ 1−3 Gyr. The fraction of late-type galaxies with a star formation activity reduced by QF > 80% and with an HI-deficiency parameter HI−def > 0.4 drops by a factor of ~5 from the inner half virial radius of the Virgo cluster (R/Rvir < 0.5), where the hot diffuse X-ray emitting gas of the cluster is located, to the outer regions (R/Rvir > 4). The efficient quenching of the star formation activity observed in Virgo suggests that the dominant stripping process is ram pressure. We discuss the implication of this result in the cosmological context of galaxy evolution.
Context. Using MegaCam at the CFHT, we obtained a deep narrow band Hα+NII wide-field image of NGC 4569 (M90), the brightest late-type galaxy in the Virgo cluster. The image reveals the presence of ...long tails of diffuse ionized gas, without any associated stellar component extending from the disc of the galaxy up to ≃80 kpc (projected distance) and with a typical surface brightness of a few 10-18 erg s-1 cm-2 arcsec-2. These features provide direct evidence that NGC 4569 is undergoing a ram-presure stripping event. The image also shows a prominent 8 kpc spur of ionized gas that is associated with the nucleus that spectroscopic data identify as an outflow. With some assumptions on the 3D distribution of the gas, we use the Hα surface brightness of these extended low-surface brightness features to derive the density and the mass of the gas that has been stripped during the interaction of the galaxy with the intracluster medium. The comparison with ad hoc chemo-spectrophotometric models of galaxy evolution indicates that the mass of the Hα emitting gas in the tail is a large fraction of that of the cold phase that has been stripped from the disc, suggesting that the gas is ionized within the tail during the stripping process. The lack of star-forming regions suggests that mechanisms other than photoionization are responsible for the excitation of the gas (shocks, heat conduction, magneto hydrodynamic waves). This analysis indicates that ram pressure stripping is efficient in massive (Mstar ≃ 1010.5 M⊙) galaxies located in intermediate-mass (≃1014 M⊙) clusters under formation. It also shows that the mass of gas expelled by the nuclear outflow is only ~1% than that removed during the ram pressure stripping event.Together these results indicate that ram pressure stripping, rather than starvation through nuclear feedback, can be the dominant mechanism that is responsible for the quenching of the star formation activity of galaxies in high density environments.
We use a volume-, magnitude-limited sample of nearby galaxies to investigate the effect of the environment on the H i scaling relations. We confirm that the H i-to-stellar mass ratio anticorrelates ...with stellar mass, stellar mass surface density and NUV −r colour across the whole range of parameters covered by our sample (109≲M
*≲ 1011 M⊙, 7.5 ≲μ*≲ 9.5 M⊙ kpc−2, 2 ≲ NUV −r≲ 6 mag). These scaling relations are also followed by galaxies in the Virgo cluster, although they are significantly offset towards lower gas content. Interestingly, the difference between field and cluster galaxies gradually decreases moving towards massive, bulge-dominated systems. By comparing our data with the predictions of chemo-spectrophotometric models of galaxy evolution, we show that starvation alone cannot explain the low gas content of Virgo spirals and that only ram-pressure stripping is able to reproduce our findings. Finally, motivated by previous studies, we investigate the use of a plane obtained from the relations between the H i-to-stellar mass ratio, stellar mass surface density and NUV −r colour as a proxy for the H i deficiency parameter. We show that the distance from the 'H i gas fraction plane' can be used as an alternative estimate for the H i deficiency, but only if carefully calibrated on pre-defined samples of 'unperturbed' systems.
In high density environments, the gas content of galaxies is stripped, leading to a rapid quenching of their star formation activity. This dramatic environmental effect, which is not related to ...typical passive evolution, is generally not taken into account in the star formation histories (SFHs) usually assumed to perform spectral energy distribution (SED) fitting of these galaxies, yielding a poor fit of their stellar emission and, consequently, biased estimate of the star formation rate (SFR). In this work, we aim at reproducing this rapid quenching using a truncated delayed SFH that we implemented in the SED fitting code CIGALE. We show that the ratio between the instantaneous SFR and the SFR just before the quenching (rSFR) is well constrained as long as rest-frame UV data are available. This SED modeling is applied to the Herschel Reference Survey (HRS) containing isolated galaxies and sources falling in the dense environment of the Virgo cluster. The latter are Hi-deficient because of ram pressure stripping. We show that the truncated delayed SFH successfully reproduces their SED, while typical SFH assumptions fail. A good correlation is found between rSFR and Hi−def, the parameter that quantifies the gas deficiency of cluster galaxies, meaning that SED fitting results can be used to provide a tentative estimate of the gas deficiency of galaxies for which Hi observations are not available. The HRS galaxies are placed on the SFR-M∗ diagram showing that the Hi-deficient sources lie in the quiescent region, thus confirming previous studies. Using the rSFR parameter, we derive the SFR of these sources before quenching and show that they were previously on the main sequence relation. We show that the rSFR parameter is also recovered well for deeply obscured high redshift sources, as well as in the absence of IR data. SED fitting is thus a powerful tool for identifying galaxies that underwent a rapid star formation quenching.
ABSTRACT We use a volume-, magnitude-limited sample of nearby galaxies to investigate the effect of the environment on the Hi scaling relations. We confirm that the Hi-to-stellar mass ratio ...anticorrelates with stellar mass, stellar mass surface density and NUV -r colour across the whole range of parameters covered by our sample (109M* 1011M,7.5 μ* 9.5Mkpc-2, 2 NUV -r 6mag). These scaling relations are also followed by galaxies in the Virgo cluster, although they are significantly offset towards lower gas content. Interestingly, the difference between field and cluster galaxies gradually decreases moving towards massive, bulge-dominated systems. By comparing our data with the predictions of chemo-spectrophotometric models of galaxy evolution, we show that starvation alone cannot explain the low gas content of Virgo spirals and that only ram-pressure stripping is able to reproduce our findings. Finally, motivated by previous studies, we investigate the use of a plane obtained from the relations between the Hi-to-stellar mass ratio, stellar mass surface density and NUV -r colour as a proxy for the Hi deficiency parameter. We show that the distance from the 'Hi gas fraction plane' can be used as an alternative estimate for the Hi deficiency, but only if carefully calibrated on pre-defined samples of 'unperturbed' systems. PUBLICATION ABSTRACT
We study the properties of the cold gas component of the interstellar medium of the Herschel Reference Survey, a complete volume-limited (15 <, ~ D <, ~ 25 Mpc), K-band-selected sample of galaxies ...spanning a wide range in morphological type (from ellipticals to dwarf irregulars) and stellar mass (10 super(9) <, ~ M sub(star) <, ~ 10 super(11) M sub(middot in circle)). The multifrequency data in our hands are used to trace the molecular gas mass distribution and the main scaling relations of the sample, which put strong constraints on galaxy formation simulations. We extend the main scaling relations concerning the total and the molecular gas component determined for massive galaxies (M sub(star) > ~ 10 super(10) M sub(middot in circle)) from the COLD GASS survey down to stellar masses M sub(star) = 10 super(9) M sub(middot in circle). As scaling variables we use the total stellar mass M sub(star), the stellar surface density mu sub(star), the specific star formation rate SSFR, and the metallicity of the target galaxies. By comparing molecular gas masses determined using a constant or a luminosity dependent X sub(CO) conversion factor, we estimate the robustness of these scaling relations on the very uncertain assumptions used to transform CO line intensities into molecular gas masses. The molecular gas distribution of a K-band-selected sample is significantly different from that of a far-infrared-selected sample since it includes a significantly smaller number of objects with M(H sub(2)) <, ~ 6 x 10 super(9) M sub(middot in circle). In spiral galaxies the molecular gas phase is only 25-30% of the atomic gas. The analysis also indicates that the slope of the main scaling relations depends on the adopted conversion factor. Among the sampled relations, all those concerning M(gas)/M sub(star) are statistically significant and show little variation with X sub(CO). We observe a significant correlation between M(H sub(2))/M sub(star) and SSFR, M(H sub(2))/M(HI ) and mu sub(star), M(H sub(2))/M(HI ) and 12 +log (O/H), regardless of the adopted X sub(CO). The total and molecular gas consumption timescales are anticorrelated with the specific star formation rate. The comparison of HRS and COLD GASS data indicates that some of the observed scaling relations are nonlinear.
The Herschel Reference Survey is a complete volume-limited, K-band-selected sample of nearby objects including Virgo cluster and isolated objects. Using a recent compilation of HI and CO data for ...this sample we study the effects of the cluster environment on the molecular gas content of spiral galaxies. With the subsample of unperturbed field galaxies, we first identify the stellar mass as the scaling variable that traces the total molecular gas mass of galaxies better. We show that, on average, HI-deficient galaxies are significantly offset (4sigma) from the M(H sub(2)) vs. M sub(star) relation for HI-normal galaxies. We use the M(H sub(2)) vs. M sub(star) scaling relation to define the H sub(2)-deficiency parameter as the difference, on logarithmic scale, between the expected and observed molecular gas mass for a galaxy of given stellar mass. The H sub(2)-deficiency parameter shows a weak and scattered relation with the HI-deficiency parameter, here taken as a proxy for galaxy interactions with the surrounding cluster environment. We also show that, as for the atomic gas, the extent of the molecular disc decreases with increasing HI-deficiency. All together, these results show that cluster galaxies have, on average, a lower molecular gas content than similar objects in the field. Our analysis indicates that ram pressure stripping is the physical process responsible for this molecular gas deficiency. The slope of the H sub(2) - def vs. HI - def relation is less than unity, while the D(HI)/D(i) vs. HI - def relation is steeper than the D(CO)/D(i) vs. HI - def relation, thereby indicating that the molecular gas is removed less efficiently than the atomic gas. This result can be understood if the atomic gas is distributed on a relatively flat disc that is more extended than the stellar disc. It is thus less anchored to the gravitational potential well of the galaxy than the molecular gas phase, which is distributed on an exponential disc with a scalelength r sub(CO) Asymptotically = to 0.2r sub(24.5) (g). There is a clear trend between the NUV-i colour index, which is a proxy for the specific star formation activity, and the H sub(2)-deficiency parameter, which suggests that molecular gas removal quenches the activity of star formation. This causes galaxies migrate from the blue cloud to the green valley and, eventually, to the red sequence. The total gas-consumption timescale of gas deficient cluster galaxies is comparable to that of isolated, unperturbed systems. The total gas depletion timescale determined by considering the recycled fraction is T sub(gas,R) Asymptotically = to 3.0-3.3 Gyr, which is significantly larger than the typical timescale for total gas removal in a ram pressure stripping process, indicated by recent hydrodynamical simulations to be T sub(RP)Asympt otically = to 1.5 Gyr. The comparison of these timescales suggests that ram pressure, rather than a simple stop of the infall of pristine gas from the halo, will be the dominant process driving the future evolution of these cluster galaxies.
We study the evolution of dwarf (L sub(H) < 10 super(9.6) L sub(H) unk) star-forming and quiescent galaxies in the Virgo Cluster by comparing their UV to radio centimetric properties to the ...predictions of multizone chemospectrophotometric models of galaxy evolution especially tuned to take into account the perturbations induced by the interaction with the cluster intergalactic medium. Our models simulate one or multiple ram pressure stripping events and galaxy starvation. Models predict that all star-forming dwarf galaxies entering the cluster for the first time loose most, if not all, of their atomic gas content, quenching on short timescales ( less than or equal to 150 Myr) their activity of star formation. These dwarf galaxies soon become red and quiescent, gas metal-rich objects with spectrophotometric and structural properties similar to those of dwarf ellipticals. Young, low-luminosity, high surface brightness star-forming galaxies such as late-type spirals and BCDs are probably the progenitors of relatively massive dwarf ellipticals, while it is likely that low surface brightness Magellanic irregulars evolve into very low surface brightness quiescent objects hardly detectable in ground-based imaging surveys. The small number of dwarf galaxies with physical properties intermediate between those of star-forming and quiescent systems is consistent with a rapid (<1 Gyr) transitional phase between the two dwarf galaxy populations. These results, combined with statistical considerations, are consistent with the idea that most of the dwarf ellipticals dominating the faint end of the Virgo luminosity function were initially star-forming systems, accreted by the cluster and stripped of their gas by one or subsequent ram pressure stripping events.
Long gamma-ray bursts (LGRBs) are associated with massive stars and are therefore linked to star formation. To reach our goal we use the Swift/BAT6 complete sample of LGRBs. In this first paper, we ...build the spectral energy distribution (SED) of the 14 z < 1 host galaxies of the BAT6 LGRB sample and determine their stellar masses (M) from SED fitting. To investigate the presence of a bias in the LGRB-star formation relation we compare the stellar mass distribution of the LGRB host galaxies (i) with star-forming galaxies observed in deep surveys (U1traVISTA) within the same redshift limit; (ii) with semi-analytical models of the z < 1 star-forming galaxy population; and (iii) with dedicated numerical simulations of LGRB hosts having different metallicity thresholds for the progenitor star environment. We find that at z < 1, LGRBs tend to avoid massive galaxies and are very powerful for selecting a population of faint low-mass star-forming galaxies, partly below the completeness limits of galaxy surveys.
Aims. We investigate the existence of a metallicity threshold for the production of long gamma-ray bursts (LGRBs). Methods. We used the host galaxies of the Swift/BAT6 sample of LGRBs. We considered ...the stellar mass, star formation rate (SFR), and metallicity determined from the host galaxy photometry and spectroscopy up to z = 2 and used them to compare the distribution of host galaxies to that of field galaxies in the mass-metallicity and fundamental metallicity relation plane. Results. We find that although LGRBs also form in galaxies with relatively large stellar masses, the large majority of host galaxies have metallicities below log (O/H) ~ 8.6. The extension to z = 2 results in a good sampling of stellar masses also above Log(M∗/M⊙) ~ 9.5 and provides evidence that LGRB host galaxies do not follow the fundamental metallicity relation. As shown by the comparison with dedicated numerical simulations of LGRB host galaxy population, these results are naturally explained by the existence of a mild (~0.7 Z⊙) threshold for the LGRB formation. The present statistics does not allow us to discriminate between different shapes of the metallicity cutoff, but the relatively high metallicity threshold found in this work is somewhat in disagreement to most of the standard single-star models for LGRB progenitors.
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