arXiv subjects

M. Symeonidis

Publications and source records attributed to M. Symeonidis.

At least 37 records · Page 2Linked to original sources

arXiv2015

Submm-bright X-ray absorbed QSOs at z~2: insights into the co-evolution of AGN and star-formation

We have assembled a sample of 5 X-ray-absorbed and submm-luminous type 1 QSOs at $z \sim 2$ which are simultaneously growing their central black holes through accretion and forming stars copiously. We present here the analysis of their rest-frame UV to submm Spectral Energy Distributions (SEDs), including new Herschel data. Both AGN (direct and reprocessed) and Star Formation (SF) emission are needed to model their SEDs. From the SEDs and their UV-optical spectra we have estimated the masses of their black holes $M_{BH}\sim 10^{9}-10^{10}\,M_{\odot}$, their intrinsic AGN bolometric luminosities $L_{BOL}\sim(0.8 - 20)\times 10^{13} L_{\odot}$, Eddington ratios $L_{BOL}/L_{Edd}\sim 0.1 - 1.1$ and bolometric corrections $L_{BOL}/L_{X,2-10}\sim 30 - 500$. These values are common among optically and X-ray-selected type 1 QSOs (except for RX~J1249), except for the bolometric corrections, which are higher. These objects show very high far-infrared luminosities $L_{FIR}\sim$ (2 - 8)$\times10^{12}\,M_{\odot}$ and Star Formation Rates SFR$\sim 1000 M_{\odot}/$y. From their $L_{FIR}$ and the shape of their FIR-submm emission we have estimated star-forming dust masses of $M_{DUST}\sim 10^9\,M_\odot$. We have found evidence of a tentative correlation between the gas column densities of the ionized absorbers detected in X-ray (N$_{H_{ion}}$) and $SFR$. Our computed black hole masses are amongst the most massive known.

astro-ph.GA↗

arXiv2014

Traces of co-evolution in high z X-ray selected and submm-luminous QSOs

We present a detailed study of a X -ray selected sample of 5 submillimeter bright QSOs at $z\sim2$, where the highest rates of star formation (SF) and further growth of black holes (BH) occur. Therefore, this sample is a great laboratory to investigate the co-evolution of star formation and AGN. We present here the analysis of the spectral energy distributions (SED) of the 5 QSOS, including new data from Herschel PACS and SPIRE. Both AGN components (direct and reprocessed) and like Star Formation (SF) are needed to model its SED. From the SED and their UV-optical spectra we have estimated the mass of the black hole ($M_{BH} = 10^9 - 10^{10} M_{SUN}$) and bolometric luminosities of AGN ($L_{BOL} = (0.8-20) \times 10^{13} L_{SUN}$). These objects show very high luminosities in the far infrared range (at the H/ULIRG levels) and very high rates of SF (SFR = 400-1400 $M_{SUN}$/y). Known their current SFR and their BH masses, we deduce that their host galaxies must be already very massive, or would not have time to get to the local relation between BH mass and bulge. Finally, we found evidence of a possible correlation between the column density of ionized gas detected in X-rays ($NH_{ion}$) and SFR, which would provide a link between AGN and SF processes.

astro-ph.GA↗

arXiv2014

Linking the X-ray and infrared properties of star-forming galaxies at z<1.5

We present the most complete study to date of the X-ray emission from star-formation in high redshift (median z=0.7; z<1.5), IR-luminous (L_IR=10^10-10^13 L_sun) galaxies detected by Herschel's PACS and SPIRE instruments. For our purpose we take advantage of the deepest X-ray data to date, the Chandra deep fields (North and South). Sources which host AGN are removed from our analysis by means of multiple AGN indicators. We find an AGN fraction of 18+/-2 per cent amongst our sample and note that AGN entirely dominate at values of log[L_X/L_IR]>-3 in both hard and soft X-ray bands. From the sources which are star-formation dominated, only a small fraction are individually X-ray detected and for the bulk of the sample we calculate average X-ray luminosities through stacking. We find an average soft X-ray to infrared ratio of log[L_SX/L_IR]=-4.3 and an average hard X-ray to infrared ratio of log[L_HX/L_IR]=-3.8. We report that the X-ray/IR correlation is approximately linear through the entire range of L_IR and z probed and, although broadly consistent with the local (z<0.1) one, it does display some discrepancies. We suggest that these discrepancies are unlikely to be physical, i.e. due to an intrinsic change in the X-ray properties of star-forming galaxies with cosmic time, as there is no significant evidence for evolution of the L_X/L_IR ratio with redshift. Instead they are possibly due to selection effects and remaining AGN contamination. We also examine whether dust obscuration in the galaxy plays a role in attenuating X-rays from star-formation, by investigating changes in the L_X/L_IR ratio as a function of the average dust temperature. We conclude that X-rays do not suffer any measurable attenuation in the host galaxy.

astro-ph.GA↗

arXiv2014

Herschel/PACS Observations of the Host Galaxy of GRB 031203

We present Herschel/PACS observations of the nearby (z=0.1055) dwarf galaxy that has hosted the long gamma ray burst (LGRB) 031203. Using the PACS data we have been able to place constraints on the dust temperature, dust mass, total infrared luminosity and infrared-derived star-formation rate (SFR) for this object. We find that the GRB host galaxy (GRBH) 031203 has a total infrared luminosity of 3x10^10 L_sun placing it in the regime of the IR-luminous galaxy population. Its dust temperature and specific SFR are comparable to that of many high-redshift (z=0.3-2.5) infrared (IR)-detected GRB hosts (T_dust>40K ; sSFR>10 Gyr^-1), however its dust-to-stellar mass ratio is lower than what is commonly seen in IR-luminous galaxies. Our results suggest that GRBH 031203 is undergoing a strong starburst episode and its dust properties are different to those of local dwarf galaxies within the same metallicity and stellar mass range. Furthermore, our measurements place it in a distinct class to the well studied nearby host of GRB 980425 (z=0.0085), confirming the notion that GRB host galaxies can span a large range in properties even at similar cosmological epochs, making LGRBs an ideal tool in selecting samples of star-forming galaxies up to high redshift.

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arXiv2014

The FMOS-COSMOS survey of star-forming galaxies at z ~ 1.6. I. Hα-based star formation rates and dust extinction

We present the first results from a near-IR spectroscopic survey of the COSMOS field, using the Fiber Multi-Object Spectrograph on the Subaru telescope, designed to characterize the star-forming galaxy population at $1.4<z<1.7$. The high-resolution mode is implemented to detect H$α$ in emission between $1.6{\rm -}1.8 \mathrm{μm}$ with $f_{\rm Hα}\gtrsim4\times10^{-17}$ erg cm$^{-2}$ s$^{-1}$. Here, we specifically focus on 271 sBzK-selected galaxies that yield a H$α$ detection thus providing a redshift and emission line luminosity to establish the relation between star formation rate and stellar mass. With further $J$-band spectroscopy for 89 of these, the level of dust extinction is assessed by measuring the Balmer decrement using co-added spectra. We find that the extinction ($0.6\lesssim A_\mathrm{Hα} \lesssim 2.5$) rises with stellar mass and is elevated at high masses compared to low-redshift galaxies. Using this subset of the spectroscopic sample, we further find that the differential extinction between stellar and nebular emission \hbox{$E_\mathrm{star}(B-V)/E_\mathrm{neb}(B-V)$} is 0.7--0.8, dissimilar to that typically seen at low redshift. After correcting for extinction, we derive an H$α$-based main sequence with a slope ($0.81\pm0.04$) and normalization similar to previous studies at these redshifts.

astro-ph.CO↗

arXiv2014

HerMES: Spectral Energy Distributions of Submillimeter Galaxies at z >4

We present a study of the infrared properties for a sample of seven spectroscopically confirmed submillimeter galaxies at $z>$4.0. By combining ground-based near-infrared, Spitzer IRAC and MIPS, Herschel SPIRE, and ground-based submillimeter/millimeter photometry, we construct their Spectral Energy Distributions (SED) and a composite model to fit the SEDs. The model includes a stellar emission component at $λ_{\rm rest} <$ 3.5$ μ$m; a hot dust component peaking at $λ_{rest} \sim$ 5$\,μ$m; and cold dust component which becomes significant for $λ_{\rm rest} >$ 50$\,μ$m. Six objects in the sample are detected at 250 and 350$ μ$m. The dust temperatures for the sources in this sample are in the range of 40$-$80 K, and their $L_{\rm FIR}$ $\sim$ 10$^{13}$ L$_{\odot}$ qualifies them as Hyper$-$Luminous Infrared Galaxies (HyperLIRGs). The mean FIR-radio index for this sample is around $< q > = 2.2$ indicating no radio excess in their radio emission. Most sources in the sample have 24$ μ$m detections corresponding to a rest-frame 4.5$ μ$m luminosity of Log$_{10}$(L$_{4.5}$ / L$_{\odot}$) = 11 $\sim$ 11.5. Their L$_{\rm 4.5}$/$L_{\rm FIR}$ ratios are very similar to those of starburst dominated submillimeter galaxies at $z \sim$ 2. The $L_{\rm CO}-L_{\rm FIR}$ relation for this sample is consistent with that determined for local ULIRGs and SMGs at $z \sim$ 2. We conclude that submillimeter galaxies at $z >$ 4 are hotter and more luminous in the FIR, but otherwise very similar to those at $z \sim$ 2. None of these sources show any sign of the strong QSO phase being triggered.

astro-ph.GA↗

arXiv2013

The evolution of the dust temperatures of galaxies in the SFR$-M_{\ast}$ plane up to $z$$\,\thicksim\,$$2$

[Abridged] We study the evolution of the dust temperatures of galaxies in the SFR-M* plane up to z~2 using observations from the Herschel Space Observatory. Starting from a sample of galaxies with reliable star-formation rates (SFRs), stellar masses (M*) and redshift estimates, we grid the SFR-M* parameter space in several redshift ranges and estimate the mean Tdust of each SFR-M*-z bin. Dust temperatures are inferred using the stacked far-infrared flux densities of our SFR-M*-z bins. At all redshifts, Tdust increases with infrared luminosities (LIR), specific SFRs (SSFR; i.e., SFR/M*) and distances with respect to the main sequence (MS) of the SFR-M* plane (i.e., D_SSFR_MS=log[SSFR(galaxy)/SSFR_MS(M*,z)]). The Tdust-SSFR and Tdust-D_SSFR_MS correlations are statistically more significant than the Tdust-LIR one. While the slopes of these three correlations are redshift-independent, their normalizations evolve from z=0 and z~2. We convert these results into a recipe to derive Tdust from SFR, M* and z. The existence of a strong Tdust-D_SSFR_MS correlation provides us with information on the dust and gas content of galaxies. (i) The slope of the Tdust-D__SSFR_MS correlation can be explained by the increase of the star-formation efficiency (SFE; SFR/Mgas) with D_SSFR_MS as found locally by molecular gas studies. (ii) At fixed D_SSFR_MS, the constant Tdust observed in galaxies probing large ranges in SFR and M* can be explained by an increase or decrease of the number of star-forming regions with comparable SFE enclosed in them. (iii) At high redshift, the normalization towards hotter temperature of the Tdust-D_SSFR_MS correlation can be explained by the decrease of the metallicities of galaxies or by the increase of the SFE of MS galaxies. All these results support the hypothesis that the conditions prevailing in the star-forming regions of MS and far-above-MS galaxies are different.

astro-ph.CO↗

arXiv2013

The incidence of obscuration in active galactic nuclei

We study the incidence of nuclear obscuration on a complete sample of 1310 AGN selected on the basis of their rest-frame 2-10 keV X-ray flux from the XMM-COSMOS survey, in the redshift range 0.3<z<3.5. We classify the AGN as obscured or un-obscured on the basis of either the optical spectral properties and the overall SED or the shape of the X-ray spectrum. The two classifications agree in about 70% of the objects, and the remaining 30% can be further subdivided into two distinct classes: at low luminosities X-ray un-obscured AGN do not always show signs of broad lines or blue/UV continuum emission in their optical spectra, most likely due to galaxy dilution effects; at high luminosities broad line AGN may have absorbed X-ray spectra, which hints at an increased incidence of small-scale (sub-parsec) dust-free obscuration. We confirm that the fraction of obscured AGN is a decreasing function of the intrinsic X-ray luminosity, while the incidence of absorption shows significant evolution only for the most luminous AGN, which appear to be more commonly obscured at higher redshift. We find no significant difference between the mean stellar masses and star formation rates of obscured and un-obscured AGN hosts. We conclude that the physical state of the medium responsible for obscuration in AGN is complex, and mainly determined by the radiation environment (nuclear luminosity) in a small region enclosed within the gravitational sphere of influence of the central black hole, but is largely insensitive to the wider scale galactic conditions.

astro-ph.CO↗

arXiv2013

HerMES: Candidate High-Redshift Galaxies Discovered with Herschel/SPIRE

We present a method for selecting $z>4$ dusty, star forming galaxies (DSFGs) using Herschel/SPIRE 250/350/500 $μm$ flux densities to search for red sources. We apply this method to 21 deg$^2$ of data from the HerMES survey to produce a catalog of 38 high-$z$ candidates. Follow-up of the first 5 of these sources confirms that this method is efficient at selecting high-$z$ DSFGs, with 4/5 at $z=4.3$ to $6.3$ (and the remaining source at $z=3.4$), and that they are some of the most luminous dusty sources known. Comparison with previous DSFG samples, mostly selected at longer wavelengths (e.g., 850 $μm$) and in single-band surveys, shows that our method is much more efficient at selecting high-$z$ DSFGs, in the sense that a much larger fraction are at $z>3$. Correcting for the selection completeness and purity, we find that the number of bright ($S_{500\,μm} \ge 30$ mJy), red Herschel sources is $3.3 \pm 0.8$ deg$^{-2}$. This is much higher than the number predicted by current models, suggesting that the DSFG population extends to higher redshifts than previously believed. If the shape of the luminosity function for high-$z$ DSFGs is similar to that at $z\sim2$, rest-frame UV based studies may be missing a significant component of the star formation density at $z=4$ to $6$, even after correction for extinction.

astro-ph.CO↗

arXiv2013

The suppression of star formation by powerful active galactic nuclei

The old, red stars which constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly from accretion onto black holes. It is widely suspected, but unproven, that the tight correlation in mass of the black hole and stellar components results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, while powerful star-forming galaxies are usually dust-obscured and are brightest at infrared to submillimetre wavelengths. Here we report observations in the submillimetre and X-ray which show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 Gyrs old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10^44 erg/s. This suppression of star formation in the host galaxies of powerful AGN is a key prediction of models in which the AGN drives a powerful outflow, expelling the interstellar medium of its host galaxy and transforming the galaxy's properties in a brief period of cosmic time.

astro-ph.CO↗

arXiv2013

HerMES: dust attenuation and star formation activity in UV-selected samples from z~4 to z~1.5

We study the link between observed ultraviolet luminosity, stellar mass, and dust attenuation within rest-frame UV-selected samples at z~ 4, 3, and 1.5. We measure by stacking at 250, 350, and 500 um in the Herschel/SPIRE images from the HerMES program the average infrared luminosity as a function of stellar mass and UV luminosity. We find that dust attenuation is mostly correlated with stellar mass. There is also a secondary dependence with UV luminosity: at a given UV luminosity, dust attenuation increases with stellar mass, while at a given stellar mass it decreases with UV luminosity. We provide new empirical recipes to correct for dust attenuation given the observed UV luminosity and the stellar mass. Our results also enable us to put new constraints on the average relation between star formation rate and stellar mass at z~ 4, 3, and 1.5. The star formation rate-stellar mass relations are well described by power laws (SFR~ M^0.7), with the amplitudes being similar at z~4 and z~3, and decreasing by a factor of 4 at z~1.5 at a given stellar mass. We further investigate the evolution with redshift of the specific star formation rate. Our results are in the upper range of previous measurements, in particular at z~3, and are consistent with a plateau at 3<z<4. Current model predictions (either analytic, semi-analytic or hydrodynamic) are inconsistent with these values, as they yield lower predictions than the observations in the redshift range we explore. We use these results to discuss the star formation histories of galaxies in the framework of the Main Sequence of star-forming galaxies. Our results suggest that galaxies at high redshift (2.5<z<4) stay around 1 Gyr on the Main Sequence. With decreasing redshift, this time increases such that z=1 Main Sequence galaxies with 10^8<M_*/Msun<10^10 stay on the Main Sequence until z=0.

astro-ph.CO↗

arXiv2013

Multi-Wavelength SEDs of Herschel Selected Galaxies in the COSMOS Field

We combine Herschel PACS and SPIRE maps of the full 2 deg^2 COSMOS field with existing multi-wavelength data to obtain template and model-independent optical-to-far-infrared spectral energy distributions (SEDs) for 4,218 Herschel-selected sources with log(L_IR/L_sun) = 9.4-13.6 and z = 0.02-3.54. Median SEDs are created by binning the optical to far-infrared (FIR) bands available in COSMOS as a function of infrared luminosity. Herschel probes rest-frame wavelengths where the bulk of the infrared radiation is emitted, allowing us to more accurately determine fundamental dust properties of our sample of infrared luminous galaxies. We find that the SED peak wavelength (lambda_peak) decreases and the dust mass (M_dust) increases with increasing total infrared luminosity (L_IR). In the lowest infrared luminosity galaxies (log(L_IR/L_sun) = 10.0-11.5), we see evidence of Polycyclic Aromatic Hydrocarbons (PAH) features (lambda=7-9 um), while in the highest infrared luminosity galaxies (L_IR > 10^12 L_sun) we see an increasing contribution of hot dust and/or power-law emission, consistent with the presence of heating from an active galactic nucleus (AGN). We study the relationship between stellar mass and star formation rate of our sample of infrared luminous galaxies and find no evidence that Herschel-selected galaxies follow the SFR/M_* "main sequence" as previously determined from studies of optically selected, star-forming galaxies. Finally, we compare the mid-infrared (MIR) to FIR properties of our infrared luminous galaxies using the previously defined diagnostic, IR8 = L_IR / L_8, and find that galaxies with L_IR > 10^11.3 L_sun tend to systematically lie above (~3-5) the IR8 "infrared main sequence", suggesting either suppressed PAH emission or an increasing contribution from AGN heating.

astro-ph.CO↗

arXiv2013

The use and calibration of read-out streaks to increase the dynamic range of the Swift Ultraviolet/Optical Telescope

The dynamic range of photon counting micro-channel-plate (MCP) intensified charged-coupled device (CCD) instruments such as the Swift Ultraviolet/Optical Telescope (UVOT) and the XMM-Newton Optical Monitor (XMM-OM) is limited at the bright end by coincidence loss, the superposition of multiple photons in the individual frames recorded by the CCD. Photons which arrive during the brief period in which the image frame is transferred for read out of the CCD are displaced in the transfer direction in the recorded images. For sufficiently bright sources, these displaced counts form read-out streaks. Using UVOT observations of Tycho-2 stars, we investigate the use of these read-out streaks to obtain photometry for sources which are too bright (and hence have too much coincidence loss) for normal aperture photometry to be reliable. For read-out-streak photometry, the bright-source limiting factor is coincidence loss within the MCPs rather than the CCD. We find that photometric measurements can be obtained for stars up to 2.4 magnitudes brighter than the usual full-frame coincidence-loss limit by using the read-out streaks. The resulting bright-limit Vega magnitudes in the UVOT passbands are UVW2=8.80, UVM2=8.27, UVW1=8.86, u=9.76, b=10.53, v=9.31 and White=11.71; these limits are independent of the windowing mode of the camera. We find that a photometric precision of 0.1 mag can be achieved through read-out streak measurements. A suitable method for the measurement of read-out streaks is described and all necessary calibration factors are given.

astro-ph.IM↗

arXiv2013

The SCUBA-2 Cosmology Legacy Survey: demographics of the 450 μm-population

We investigate the multi-wavelength properties of a sample of 450-μm selected sources from the SCUBA-2 Cosmology Legacy Survey (S2CLS). A total of 69 sources were identified above 4σ in deep SCUBA-2 450-μm observations overlapping the UDS and COSMOS fields and covering 210 sq. arcmin to a typical depth of σ450=1.5 mJy. Reliable cross identification are found for 58 sources (84 per cent) in Spitzer and Hubble Space Telescope WFC3/IR data. The photometric redshift distribution (dN/dz) of 450μm-selected sources is presented, showing a broad peak in the redshift range 1 =10^12 +/- 0.8 L_sol, =42 +/- 11 K and <β_D>=1.6 +/- 0.5, respectively. The relationship between these SED parameters and the physical properties of galaxies is investigated, revealing correlations between T_D and LIR and between β_D and both stellar mass and effective radius. The connection between star formation rate and stellar mass is explored, with 24 per cent of 450 μm sources found to be ``star-bursts'', i.e. displaying anomalously high specific SFRs. However, both the number density and observed properties of these ``star-burst'' galaxies are found consistent with the population of normal star-forming galaxies.

astro-ph.CO↗

arXiv2013

Far-IR Emission From Dust-Obscured Galaxies

Dust-obscured galaxies (DOGs) are a UV-faint, IR-bright galaxy population that reside at z~2 and are believed to be in a phase of dusty star-forming and AGN activity. We present far-IR observations of a complete sample of DOGs in the 2 deg2 of COSMOS. The 3077 DOGs have =1.9+/-0.3 and are selected from 24um and r+ observations using a color cut of r+ - [24]>=7.5 (AB mag) and S24>=100uJy. Based on the near-IR SEDs, 47% are star-formation dominated and 10% are AGN-dominated. We use SPIRE far-IR photometry from HerMES to calculate the IR luminosity and characteristic dust temperature for the 1572 (51%) DOGs that are detected at 250um (>=3σ). For the remaining 1505 (49%) that are undetected, we perform a median stacking analysis to probe fainter luminosities. Detected and undetected DOGs have average IR luminosities of (2.8+/-0.4) x 1012 LSun and (0.77+-0.08)x10^12LSun, and dust temperatures of 34+/-7 K and 37+/-3 K, respectively. The IR luminosity function of DOGs with S24>=100uJy is calculated, using far-IR observations and stacking. DOGs contribute 10-30% to the total star formation rate density of the Universe at z=1.5-2.5, dominated by 250um detected and bump DOGs. For comparison, DOGs contribute 30% to the star-formation rate density of the Universe for all galaxies at z=1.5-2.5 with S24>=100uJy. DOGs have a large scatter about the star-formation main sequence and their specific star-formation rates show that the observed phase of star-formation could be responsible for their observed stellar mass at z~2.

astro-ph.CO↗

arXiv2013

The Herschel PEP/HerMES Luminosity Function. I: Probing the Evolution of PACS selected Galaxies to z~4

We exploit the deep and extended far infrared data sets (at 70, 100 and 160 um) of the Herschel GTO PACS Evolutionary Probe (PEP) Survey, in combination with the HERschel Multi tiered Extragalactic Survey (HerMES) data at 250, 350 and 500 um, to derive the evolution of the restframe 35 um, 60 um, 90 um, and total infrared (IR) luminosity functions (LFs) up to z~4. We detect very strong luminosity evolution for the total IR LF combined with a density evolution. In agreement with previous findings, the IR luminosity density increases steeply to z~1, then flattens between z~1 and z~3 to decrease at z greater than 3. Galaxies with different SEDs, masses and sSFRs evolve in very different ways and this large and deep statistical sample is the first one allowing us to separately study the different evolutionary behaviours of the individual IR populations contributing to the IR luminosity density. Galaxies occupying the well established SFR/stellar mass main sequence (MS) are found to dominate both the total IR LF and luminosity density at all redshifts, with the contribution from off MS sources (0.6 dex above MS) being nearly constant (~20% of the total IR luminosity density) and showing no significant signs of increase with increasing z over the whole 0.8<z<2.2 range. Sources with mass in the 10< log(M/Msun) <11 range are found to dominate the total IR LF, with more massive galaxies prevailing at the bright end of the high-z LF. A two-fold evolutionary scheme for IR galaxies is envisaged: on the one hand, a starburst-dominated phase in which the SMBH grows and is obscured by dust, is followed by an AGN dominated phase, then evolving toward a local elliptical. On the other hand, moderately starforming galaxies containing a low-luminosity AGN have various properties suggesting they are good candidates for systems in a transition phase preceding the formation of steady spiral galaxies.

astro-ph.CO↗

arXiv2013

Herschel reveals the obscured star formation in HiZELS Hα emitters at z=1.47

We describe the far-infrared (FIR; rest-frame 8--1000μm) properties of a sample of 443 Hα-selected star-forming galaxies in the COSMOS and UDS fields detected by the HiZELS imaging survey. Sources are identified using narrow-band filters in combination with broad-band photometry to uniformly select Hα (and [OII] if available) emitters in a narrow redshift slice at z = 1.47+/-0.02. We use a stacking approach in Spitzer, Herschel (from PEP and HerMES surveys) and AzTEC images to describe their typical FIR properties. We find that HiZELS galaxies with observed Hα luminosities of ~ 10^{8.1-9.1} Lo have bolometric FIR luminosities of typical LIRGs, L_FIR ~ 10^{11.48+/-0.05} Lo. Combining the Hα and FIR luminosities, we derive median SFR = 32+/-5 Mo/yr and Hα extinctions of A(Hα) = 1.0+/-0.2 mag. Perhaps surprisingly, little difference is seen in typical HiZELS extinction levels compared to local star-forming galaxies. We confirm previous empirical stellar mass (M*) to A(Hα) relations and the little or no evolution up to z = 1.47. For HiZELS galaxies, we provide an empirical parametrisation of the SFR as a function of (u-z)_rest colours and 3.6μm photometry. We find that the observed Hα luminosity is a dominant SFR tracer when (u-z)_rest ~< 0.9 mag or when 3.6μm photometry > 22 mag (Vega) or when M* < 10^9.7 Mo. We do not find any correlation between the [OII]/Hα and FIR luminosity, suggesting that this emission line ratio does not trace the extinction of the most obscured star-forming regions. The luminosity-limited HiZELS sample tends to lie above of the so-called `main sequence' for star-forming galaxies, especially at low M*. This work suggests that obscured star formation is linked to the assembly of M*, with deeper potential wells in massive galaxies providing dense, heavily obscured environments in which stars can form rapidly.

astro-ph.CO↗

arXiv2013

HerMES: Cosmic Infrared Background Anisotropies and the Clustering of Dusty Star-Forming Galaxies

We present measurements of the auto- and cross-frequency power spectra of the cosmic infrared background (CIB) at 250, 350, and 500um (1200, 860, and 600 GHz) from observations totaling ~ 70 deg^2 made with the SPIRE instrument aboard the Herschel Space Observatory. We measure a fractional anisotropy dI / I = 14 +- 4%, detecting signatures arising from the clustering of dusty star-forming galaxies in both the linear (2-halo) and non-linear (1-halo) regimes; and that the transition from the 2- to 1-halo terms, below which power originates predominantly from multiple galaxies within dark matter halos, occurs at k_theta ~ 0.1 - 0.12 arcmin^-1 (l ~ 2160 - 2380), from 250 to 500um. New to this paper is clear evidence of a dependence of the Poisson and 1-halo power on the flux-cut level of masked sources --- suggesting that some fraction of the more luminous sources occupy more massive halos as satellites, or are possibly close pairs. We measure the cross-correlation power spectra between bands, finding that bands which are farthest apart are the least correlated, as well as hints of a reduction in the correlation between bands when resolved sources are more aggressively masked. In the second part of the paper we attempt to interpret the measurements in the framework of the halo model. With the aim of fitting simultaneously with one model the power spectra, number counts, and absolute CIB level in all bands, we find that this is achievable by invoking a luminosity-mass relationship, such that the luminosity-to-mass ratio peaks at a particular halo mass scale and declines towards lower and higher mass halos. Our best-fit model finds that the halo mass which is most efficient at hosting star formation in the redshift range of peak star-forming activity, z ~ 1-3, is log(M_peak/M_sun) ~ 12.1 +- 0.5, and that the minimum halo mass to host infrared galaxies is log(M_min/M_sun) ~ 10.1 +- 0.6.

astro-ph.CO↗