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Register a new userInvestigating the delay between dust radiation and star-formation in local and distant quenching galaxies
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We investigate the timescale with which the IR luminosity decreases after a complete and rapid quenching of star formation using observations of local and high-redshift galaxies. From SED modelling, we derive the time since quenching of a subsample of 14 galaxies from the Herschel Reference Survey suffering from ram-pressure stripping due to the environment of the Virgo cluster and of a subsample of 7 rapidly quenched COSMOS galaxies selected through a state-of-the-art statistical method already tested on the determination of galaxies star formation history. Three out of the 7 COSMOS galaxies have an optical spectra with no emission line, confirming their quenched nature. Present physical properties of the two samples are obtained as well as the past L$_{IR}$ of these galaxies, just before their quenching, from the long-term SFH properties. This past L$_{IR}$ is shown to be consistent with the L$_{IR}$ of reference samples of normally star-forming galaxies with same $M_*$ and $z$ than each of our quenched galaxies. We put constraints on the present to past L$_{IR}$ ratio as a function of quenching time. The two samples probe different dynamical ranges in terms of quenching age with the HRS galaxies exhibiting longer timescales (0.2-3,Gyr) compared to the COSMOS one ($<100$,Myr). Assuming an exponential decrease of the L$_{IR}$ after quenching, the COSMOS quenched galaxies are consistent with short e-folding times less than a couple of hundreds of Myr while the properties of the HRS quenched galaxies are compatible with timescales of several hundreds of Myr. For the HRS sample, this result is consistent with ram pressure stripping due to the environment. For the COSMOS sample, different quenching processes are acting on short to intermediate timescales. Processes such as galaxy mergers, disk instabilities or environmental effects can produce such strong star formation variability.
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We present the results of an observing program with the SCUBA bolometer array to measure the submillimetre (submm) dust continuum emission of 24 distant (z > 1) radio galaxies. We detected submm emission in 12 galaxies with S/N > 3, including 9 detections at z > 3. When added to previous published results these data almost triple the number of radio galaxies with z > 3 detected in the submm and yield a sample of 69 observed radio galaxies over the redshift range z = 1-5. We find that the range in rest-frame far-infrared luminosities is about a factor of 10. We have investigated the origin of this dispersion, correlating the luminosities with radio source power, size, spectral index, K-band magnitude and Lya luminosity. No strong correlations are apparent in the combined data set. We confirm and strengthen the result from previous submm observations of radio galaxies that the detection rate is a strong function of redshift. We compare the redshift dependence of the submm properties of radio galaxies with those of quasars and find that for both classes of objects the observed submm flux density increases with redshift to z ~ 4, beyond which, for the galaxies, we find tentative evidence for a decline. We find evidence for an anti-correlation between submm luminosity and UV polarisation fraction, for a subsample of 13 radio galaxies, indicating that starbursts are the dominant source of heating for dust in radio galaxies.
We combine orbital information from N-body simulations with an analytic model for star formation quenching and SDSS observations to infer the differential effect of the group/cluster environment on star formation in satellite galaxies. We also consider a model for gas stripping, using the same input supplemented with HI fluxes from the ALFALFA survey. The models are motivated by and tested on the Hydrangea cosmological hydrodynamical simulation suite. We recover the characteristic times when satellite galaxies are stripped and quenched. Stripping in massive ($M_mathrm{ vir}sim 10^{14.5},mathrm{M}_odot$) clusters typically occurs at or just before the first pericentric passage. Lower mass ($sim10^{13.5},mathrm{M}_odot$) groups strip their satellites on a significantly longer (by $sim3,mathrm{Gyr}$) timescale. Quenching occurs later: Balmer emission lines typically fade $sim3.5,mathrm{Gyr}$ ($5.5,mathrm{Gyr}$) after first pericentre in clusters (groups), followed a few hundred $mathrm{Myr}$ later by reddenning in $(g-r)$ colour. These `delay timescales are remarkably constant across the entire satellite stellar mass range probed ($sim10^{9.5}-10^{11},mathrm{M}_odot$), a feature closely tied to our treatment of `group pre-processing. The lowest mass groups in our sample ($sim10^{12.5},mathrm{M}_odot$) strip and quench their satellites extremely inefficiently: typical timescales may approach the age of the Universe. Our measurements are qualitatively consistent with the `delayed-then-rapid quenching scenario advocated for by several other studies, but we find significantly longer delay times. Our combination of a homogeneous analysis and input catalogues yields new insight into the sequence of events leading to quenching across wide intervals in host and satellite mass.
[ABRIDGED] We derive the dust properties for 753 local galaxies and examine how these relate to some of their physical properties. We model their global dust-SEDs, treated statistically as an ensemble within a hierarchical Bayesian dust-SED modeling approach. The model-derived properties are the dust masses (Mdust), the average interstellar radiation field intensities (Uav), the mass fraction of very small dust grains (QPAH fraction), as well as their standard deviations. In addition, we use mid-IR observations to derive SFR and Mstar, quantities independent of the modeling. We derive distribution functions of the properties for the galaxy ensemble and per galaxy type. The mean value of Mdust for the ETGs is lower than that for the LTGs and IRs, despite ETGs and LTGs having Mstar spanning across the whole range observed. The Uav and QPAH fraction show no difference among different galaxy types. When fixing Uav to the Galactic value, the derived QPAH fraction varies across the Galactic value (0.071). The sSFR increases with galaxy type, while this is not the case for the dust-sSFR (=SFR/Mdust), showing an almost constant SFE per galaxy type. The galaxy sample is characterised by a tight relation between Mdust and Mstar for the LTGs and Irs, while ETGs scatter around this relation and tend towards smaller Mdust. While the relation indicates that Mdust may fundamentally be linked to Mstar, metallicity and Uav are the second parameter driving the scatter, which we investigate in a forthcoming work. We use the extended KS law to estimate Mgas and the GDR. The Mgas derived from the extended KS law is on average ~20% higher than that derived from the KS law, and a large standard deviation indicates the importance of the average SF present to regulate star formation and gas supply. The average GDR for the LTGs and IRs is 370, while including the ETGs gives an average of 550. [ABRIDGED]
We explore the connection between dust and star formation, in the context of environmental effects on galaxy evolution. In particular, we exploit the susceptibility of dust to external processes to assess the influence of dense environment on star-forming galaxies. We have selected cluster Abell 1758 from the Local Cluster Substructure Survey (LoCuSS). Its complex dynamical state is an ideal test-bench to track dust removal and destruction in galaxies due to merger and accretion shocks. We present a systematic panchromatic study (from 0.15 $rm mu$m with GALEX to 500 $rm mu$m with Herschel) of spectroscopically confirmed star-forming cluster galaxies at intermediate redshift. We observe that the main subclusters (A1758N and A1758S) belong to two separate large-scale structures, with no overlapping galaxy members. Star-forming cluster members are distributed preferentially outside cluster central regions, and are not grouped in substructures. Rather, these galaxies are being funneled towards the main subclusters along separate accretion filaments. Additionally, we present the first study of dust-to-stellar (DTS) mass ratio used as indicator for local environmental influence on galaxy evolution. Star-forming cluster members show lower mean values (32% at 2.4$rm sigma$) of DTS mass ratio and lower levels of infrared emission from birth clouds with respect to coeval star-forming field galaxies. This picture is consistent with the majority of star-forming cluster members infalling in isolation. Upon accretion, star-formation is observed to decrease and warm dust is destroyed due to heating from the intracluster medium radiation, ram-pressure stripping and merger shocks.
We have used near-ultraviolet (NUV) to mid-infrared (MIR) composite spectral energy distributions (SEDs) to simultaneously model the attenuated stellar and dust emission of 0.5 < z < 2.0 galaxies. These composite SEDs were previously constructed from the photometric catalogs of the NEWFIRM Medium-Band Survey, by stacking the observed photometry of galaxies that have similar rest-frame NUV-to-NIR SEDs. In this work, we include a stacked MIPS 24 micron measurement for each SED type to extend the SEDs to rest-frame MIR wavelengths. Consistent with previous studies, the observed MIR emission for most SED types is higher than expected from only the attenuated stellar emission. We fit the NUV-to-MIR composite SEDs by the Flexible Stellar Population Synthesis (SPS) models, which include both stellar and dust emission. We compare the best-fit star formation rates (SFRs) to the SFRs based on simple UV+IR estimators. Interestingly, the UV and IR luminosities overestimate SFRs - compared to the model SFRs - by more than ~ 1 dex for quiescent galaxies, while for the highest star-forming galaxies in our sample the two SFRs are broadly consistent. The difference in specific SFRs also shows a gradually increasing trend with declining specific SFR, implying that quiescent galaxies have even lower specific SFRs than previously found. Contributions from evolved stellar populations to both the UV and the MIR SEDs most likely explain the discrepancy. Based on this work, we conclude that SFRs should be determined from modeling the attenuated stellar and dust emission simultaneously, instead of employing simple UV+IR-based SFR estimators.
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