arXiv subjects

A. Omont

Publications and source records attributed to A. Omont.

At least 55 records · Page 3Linked to original sources

arXiv2017

High dense gas fraction in intensely star-forming dusty galaxies at high redshift

We present ALMA and VLA detections of the dense molecular gas tracers HCN, HCO$^+$ and HNC in two lensed, high-redshift starbursts selected from the {\it Herschel}-ATLAS survey: {\it H}-ATLAS\,J090740.0$-$004200 (SDP.9, $z \sim 1.6$) and {\it H}-ATLAS\,J091043.1$-$000321 (SDP.11, $z \sim 1.8$). ALMA observed the $J = 3-2$ transitions in both sources, while the VLA observed the $J = 1-0$ transitions in SDP.9. We have detected all observed HCN and HCO$^+$ lines in SDP.9 and SDP.11, and also HNC(3--2) in SDP.9. The amplification factors for both galaxies have been determined from sub-arcsec resolution CO and dust emission observations carried out with NOEMA and the SMA. The HNC(1--0)/HCN(1--0) line ratio in SDP.9 suggests the presence of photon-dominated regions, as it happens to most local (U)LIRGs. The CO, HCN and HCO$^+$ SLEDs of SDP.9 are compatible to those found for many local, infrared (IR) bright galaxies, indicating that the molecular gas in local and high-redshift dusty starbursts can have similar excitation conditions. We obtain that the correlation between total IR ($L_{\rm IR}$) and dense line ($L_{\rm dense}$) luminosity in SDP.9 and SDP.11 and local star-forming galaxies can be represented by a single relation. The scatter of the $L_{\rm IR} - L_{\rm dense}$ correlation, together with the lack of sensitive dense molecular gas tracer observations for a homogeneous sample of high-redshift galaxies, prevents us from distinguishing differential trends with redshift. Our results suggest that the intense star formation found in some high-redshift dusty, luminous starbursts is associated with more massive dense molecular gas reservoirs and higher dense molecular gas fractions.

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arXiv2016

The Herschel-ATLAS: a sample of 500μm-selected lensed galaxies over 600 square degrees

We present a sample of 80 candidate strongly lensed galaxies with flux density above 100mJy at 500μm extracted from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS), over an area of 600 square degrees. Available imaging and spectroscopic data allow us to confirm the strong lensing in 20 cases and to reject it in one case. For other 8 objects the lensing scenario is strongly supported by the presence of two sources along the same line of sight with distinct photometric redshifts. The remaining objects await more follow-up observations to confirm their nature. The lenses and the background sources have median redshifts z_L = 0.6 and z_S = 2.5, respectively, and are observed out to z_L = 1.2 and z_S = 4.2. We measure the number counts of candidate lensed galaxies at 500μm and compare them with theoretical predictions, finding a good agreement for a maximum magnification of the background sources in the range 10-20. These values are consistent with the magnification factors derived from the lens modelling of individual systems. The catalogue presented here provides sub- mm bright targets for follow-up observations aimed at exploiting gravitational lensing to study with un-precedented details the morphological and dynamical properties of dusty star forming regions in z >~ 1.5 galaxies.

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arXiv2016

The space density of luminous dusty star-forming galaxies at $z>4$: SCUBA-2 and LABOCA imaging of ultrared galaxies from $Herschel$-ATLAS

Until recently, only a handful of dusty, star-forming galaxies (DSFGs) were known at $z>4$, most of them significantly amplified by gravitational lensing. Here, we have increased the number of such DSFGs substantially, selecting galaxies from the uniquely wide 250-, 350- and 500-$μ$m Herschel-ATLAS imaging survey on the basis of their extremely red far-infrared colors and faint 350- and 500-$μ$m flux densities - ergo they are expected to be largely unlensed, luminous, rare and very distant. The addition of ground-based continuum photometry at longer wavelengths from the JCMT and APEX allows us to identify the dust peak in their SEDs, better constraining their redshifts. We select the SED templates best able to determine photometric redshifts using a sample of 69 high-redshift, lensed DSFGs, then perform checks to assess the impact of the CMB on our technique, and to quantify the systematic uncertainty associated with our photometric redshifts, $σ=0.14\,(1+z)$, using a sample of 25 galaxies with spectroscopic redshifts, each consistent with our color selection. For Herschel-selected ultrared galaxies with typical colors of $S_{500}/S_{250}\sim 2.2$ and $S_{500}/S_{350}\sim 1.3$ and flux densities, $S_{500}\sim 50\,$mJy, we determine a median redshift, $\hat{z}_{\rm phot}=3.66$, an interquartile redshift range, 3.30$-$4.27, with a median rest-frame 8$-$1000-$μ$m luminosity, $\hat{L}_{\rm IR}$, of $1.3\times 10^{13}\,$L$_\odot$. A third lie at $z>4$, suggesting a space density, $ρ_{z>4}$, of $\approx 6 \times 10^{-7}\,$Mpc$^{-3}$. Our sample contains the most luminous known star-forming galaxies, and the most over-dense cluster of starbursting proto-ellipticals yet found.

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arXiv2016

Submillimeter H2O and H2O+ emission in lensed ultra- and hyper-luminous infrared galaxies at z ~ 2-4

(abridged) We report rest-frame submillimeter H2O emission line observations of 11 HyLIRGs/ULIRGs at z~2-4 selected among the brightest lensed galaxies discovered in the Herschel-ATLAS. Using the IRAM NOEMA, we have detected 14 new H2O emission lines. The apparent luminosities of the H2O emission lines are $μL_{\rm{H_2O}} \sim 6-21 \times 10^8 L_\odot$, with velocity-integrated line fluxes ranging from 4-15 Jy km s$^{-1}$. We have also observed CO emission lines using EMIR on the IRAM 30m telescope in seven sources. The velocity widths for CO and H2O lines are found to be similar. With almost comparable integrated flux densities to those of the high-J CO line, H2O is found to be among the strongest molecular emitters in high-z Hy/ULIRGs. We also confirm our previously found correlation between luminosity of H2O ($L_{\rm{H_2O}}$) and infrared ($L_{\rm{IR}}$) that $L_{\rm{H_2O}} \sim L_{\rm{IR}}^{1.1-1.2}$, with our new detections. This correlation could be explained by a dominant role of far-infrared (FIR) pumping in the H2O excitation. Modelling reveals the FIR radiation fields have warm dust temperature $T_\rm{warm}$~45-75 K, H2O column density per unit velocity interval $N_{\rm{H_2O}}/ΔV \gtrsim 0.3 \times 10^{15}$ cm$^{-2}$ km$^{-1}$ s and 100 $μ$m continuum opacity $τ_{100} > 1$ (optically thick), indicating that H2O is likely to trace highly obscured warm dense gas. However, further observations of $J\geq4$ H2O lines are needed to better constrain the continuum optical depth and other physical conditions of the molecular gas and dust. We have also detected H2O+ emission in three sources. A tight correlation between $L_{\rm{H_2O}}$ and $L_{\rm{H_2O^+}}$ has been found in galaxies from low to high redshift. The velocity-integrated flux density ratio between H2O+ and H2O suggests that cosmic rays generated by strong star formation are possibly driving the H2O+ formation.

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arXiv2016

H-ATLAS: A Candidate High Redshift Cluster/Protocluster of Star-Forming Galaxies

We investigate the region around the Planck-detected z=3.26 gravitationally lensed galaxy HATLAS J114637.9-001132 (hereinafter HATLAS12-00) using both archival Herschel data from the H-ATLAS survey and using submm data obtained with both LABOCA and SCUBA2. The lensed source is found to be surrounded by a strong overdensity of both Herschel-SPIRE sources and submm sources. We detect 17 bright (S_870 >~7 mJy) sources at >4sigma closer than 5 arcmin to the lensed object at 850/870 microns. Ten of these sources have good cross-identifications with objects detected by Herschel-SPIRE which have redder colours than other sources in the field, with 350 micron flux > 250 micron flux, suggesting that they lie at high redshift. Submillimeter Array (SMA) observations localise one of these companions to ~1 arcsecond, allowing unambiguous cross identification with a 3.6 and 4.5 micron Spitzer source. The optical/near-IR spectral energy distribution (SED) of this source is measured by further observations and found to be consistent with z>2, but incompatible with lower redshifts. We conclude that this system may be a galaxy cluster/protocluster or larger scale structure that contains a number of galaxies undergoing starbursts at the same time.

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arXiv2016

Candidate Gravitationally Lensed Dusty Star-forming Galaxies in the Herschel Wide Area Surveys

We present a list of candidate gravitationally lensed dusty star-forming galaxies (DSFGs) from the HerMES Large Mode Survey (HeLMS) and the Herschel Stripe 82 Survey (HerS). Together, these partially overlapping surveys cover 372 deg$^{2}$ on the sky. After removing local spiral galaxies and known radio-loud blazars, our candidate list of lensed DSFGs is composed of 77 sources with 500 $μ$m flux densities ($S_{500}$) greater than 100 mJy. Such sources are dusty starburst galaxies similar to the first bright Sub Millimeter Galaxies (SMGs) discovered with SCUBA. We expect a large fraction of this list to be strongly lensed, with a small fraction made up of bright SMG-SMG mergers that appear as Hyper-Luminous Infrared Galaxies (HyLIRGs; $\rm L_{IR}>10^{13} L_{\odot}$). Thirteen of the 77 candidates have spectroscopic redshifts from CO spectroscopy with ground-based interferometers, putting them at $z>1$ and well above the redshift of the foreground lensing galaxies. The surface density of our sample is 0.21 $\pm$ 0.03 deg$^{-2}$. We present follow-up imaging of a few of the candidates confirming their lensing nature. The sample presented here is an ideal tool for higher resolution imaging and spectroscopic observations to understand detailed properties of starburst phenomena in distant galaxies.

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arXiv2016

ALMA Finds Dew Drops in the Dusty Spider's Web

We present 0."5 resolution ALMA detections of the observed 246GHz continuum, [CI]^3P_2-^3P_1 fine structure line ([CI]2-1), CO(7-6) and H2O lines in the z=2.161 radio galaxy MRC1138-262, the 'Spiderweb Galaxy'. We detect strong [CI]2-1 emission both at the position of the radio core, and in a second component ~4kpc away from it. The 1100km/s broad [CI]2-1 line in this latter component, combined with its H2 mass of 1.6x10^10Msun implies this emission must come from a compact region <60pc, possibly containing a second AGN. The combined H2 mass derived for both objects using the [CI]2-1 emission is 3.3x10^10Msun. The total CO(7-6)/[CI]2-1 line flux ratio of 0.2 suggests a low excitation molecular gas reservoir and/or enhanced atomic carbon in cosmic-ray dominated regions. We detect spatially-resolved H2O 2_{11}-2_{02} emission - for the first time in a high-z un-lensed galaxy - near the outer radio lobe to the east, and near the bend of the radio jet to the west of the radio galaxy. No underlying 246GHz continuum emission is seen at either position. We suggest that the H2O emission is excited in the cooling region behind slow (10-40km/s) shocks in dense molecular gas (10^{3-5} cm^-3). The extended water emission is likely evidence of the radio jet's impact in cooling and forming molecules in the post-shocked gas in the halo and inter-cluster gas similar to what is seen in low-z clusters and other high-z radio galaxies. These observations imply that the passage of the radio jet in the interstellar and inter-cluster medium not only heats gas to high temperatures as is commonly assumed or found in simulations, but also induces cooling and dissipation which can lead to substantial amounts of cold dense molecular gas. The formation of molecules and strong dissipation in the halo gas of MRC1138-262 may explain both the extended diffuse molecular gas and young stars observed around MRC1138-262.

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arXiv2015

The HerMES sub-millimetre local and low-redshift luminosity functions

We used wide area surveys over 39 deg$^2$ by the HerMES collaboration, performed with the Herschel Observatory SPIRE multi-wavelength camera, to estimate the low-redshift, $0.02<z<0.5$, monochromatic luminosity functions (LFs) of galaxies at 250, 350 and 500$\,μ$m. SPIRE flux densities were also combined with Spitzer photometry and multi-wavelength archival data to perform a complete SED fitting analysis of SPIRE detected sources to calculate precise k-corrections, as well as the bolometric infrared (8-1000$\,μ$m) luminosity functions and their low-$z$ evolution from a combination of statistical estimators. Integration of the latter prompted us to also compute the local luminosity density (LLD) and the comoving star formation rate density (SFRD) for our sources, and to compare them with theoretical predictions of galaxy formation models. The luminosity functions show significant and rapid luminosity evolution already at low redshifts, $0.02<z<0.2$, with L$_{IR}^* \propto (1+z)^{6.0\pm0.4}$ and $Φ_{IR}^* \propto (1+z)^{-2.1\pm0.4}$, L$_{250}^* \propto (1+z)^{5.3\pm0.2}$ and $Φ_{250}^* \propto (1+z)^{-0.6\pm0.4}$ estimated using the IR bolometric and the 250$\,μ$m LFs respectively. Converting our IR LD estimate into an SFRD assuming a standard Salpeter IMF and including the unobscured contribution based on the UV dust-uncorrected emission from local galaxies, we estimate a SFRD scaling of SFRD$_0+0.08 z$, where SFRD$_0\simeq (1.9\pm 0.03)\times 10^{-2} [\mathrm{M}_\odot\,\mathrm{Mpc}^{-3}]$ is our total SFRD estimate at $z\sim0.02$.

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arXiv2015

Probing star formation in the dense environments of z~1 lensing halos aligned with dusty star-forming galaxies detected with the South Pole Telescope

We probe star formation in the environments of massive $\sim10^{13}\,M_{\odot}$ dark matter halos at redshifts of $z$$\sim$$1$. This star formation is linked to a sub-millimetre clustering signal which we detect in maps of the Planck High Frequency Instrument that are stacked at the positions of a sample of high-redshift ($z$$>$$2$) strongly-lensed dusty star-forming galaxies (DSFGs) selected from the South Pole Telescope (SPT) 2500 deg$^2$ survey. The clustering signal has sub-millimetre colours which are consistent with the mean redshift of the foreground lensing halos ($z$$\sim$$1$). We report a mean excess of star formation rate (SFR) compared to the field, of $(2700\pm700)\,M_{\odot}\,{yr}^{-1}$ from all galaxies contributing to this clustering signal within a radius of 3.5' from the SPT DSFGs. The magnitude of the Planck excess is in broad agreement with predictions of a current model of the cosmic infrared background. The model predicts that 80$\%$ of the excess emission measured by Planck originates from galaxies lying in the neighbouring halos of the lensing halo. Using Herschel maps of the same fields, we find a clear excess, relative to the field, of individual sources which contribute to the Planck excess. The mean excess SFR compared to the field is measured to be ($370\pm40)$$\,M_{\odot}\,{yr}^{-1}$ per resolved, clustered source. Our findings suggest that the environments around these massive $z$$\sim$$1$ lensing halos host intense star formation out to about $2\,$Mpc. The flux enhancement due to clustering should also be considered when measuring flux densities of galaxies in Planck data.

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arXiv2015

What Powers Lyman alpha Blobs?

Lyman alpha blobs (LABs) are spatially extended lyman alpha nebulae seen at high redshift. The origin of Lyman alpha emission in the LABs is still unclear and under debate. To study their heating mechanism(s), we present Australia Telescope Compact Array (ATCA) observations of the 20 cm radio emission and Herschel PACS and SPIRE measurements of the far-infrared (FIR) emission towards the four LABs in the protocluster J2143-4423 at z=2.38. Among the four LABs, B6 and B7 are detected in the radio with fluxes of 67+/-17 microJy and 77+/-16 microJy, respectively, and B5 is marginally detected at 3 sigma (51+/-16 microJy). For all detected sources, their radio positions are consistent with the central positions of the LABs. B6 and B7 are obviously also detected in the FIR. By fitting the data with different templates, we obtained redshifts of 2.20$^{+0.30}_{-0.35}$ for B6 and 2.20$^{+0.45}_{-0.30}$ for B7 which are consistent with the redshift of the lyman alpha emission within uncertainties, indicating that both FIR sources are likely associated with the LABs. The associated FIR emission in B6 and B7 and high star formation rates strongly favor star formation in galaxies as an important powering source for the lyman alpha emission in both LABs. However, the other two, B1 and B5, are predominantly driven by the active galactic nuclei or other sources of energy still to be specified, but not mainly by star formation. In general, the LABs are powered by quite diverse sources of energy.

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arXiv2015

Planck's Dusty GEMS: Gravitationally lensed high-redshift galaxies discovered with the Planck survey

We present an analysis of 11 bright far-IR/submm sources discovered through a combination of the Planck survey and follow-up Herschel-SPIRE imaging. Each source has a redshift z=2.2-3.6 obtained through a blind redshift search with EMIR at the IRAM 30-m telescope. Interferometry obtained at IRAM and the SMA, and optical/near-infrared imaging obtained at the CFHT and the VLT reveal morphologies consistent with strongly gravitationally lensed sources. Additional photometry was obtained with JCMT/SCUBA-2 and IRAM/GISMO at 850 um and 2 mm, respectively. All objects are bright, isolated point sources in the 18 arcsec beam of SPIRE at 250 um, with spectral energy distributions peaking either near the 350 um or the 500 um bands of SPIRE, and with apparent far-infrared luminosities of up to 3x10^14 L_sun. Their morphologies and sizes, CO line widths and luminosities, dust temperatures, and far-infrared luminosities provide additional empirical evidence that these are strongly gravitationally lensed high-redshift galaxies. We discuss their dust masses and temperatures, and use additional WISE 22-um photometry and template fitting to rule out a significant contribution of AGN heating to the total infrared luminosity. Six sources are detected in FIRST at 1.4 GHz. Four have flux densities brighter than expected from the local far-infrared-radio correlation, but in the range previously found for high-z submm galaxies, one has a deficit of FIR emission, and 6 are consistent with the local correlation. The global dust-to-gas ratios and star-formation efficiencies of our sources are predominantly in the range expected from massive, metal-rich, intense, high-redshift starbursts. An extensive multi-wavelength follow-up programme is being carried out to further characterize these sources and the intense star-formation within them.

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arXiv2014

Imaging the environment of a z = 6.3 submillimeter galaxy with SCUBA-2

We describe a search for submillimeter emission in the vicinity of one of the most distant, luminous galaxies known, HerMES FLS3 at z=6.34, exploiting it as a signpost to a potentially biased region of the early Universe, as might be expected in hierarchical structure formation models. Imaging to the confusion limit with the innovative, wide-field submillimeter bolometer camera, SCUBA-2, we are sensitive to colder and/or less luminous galaxies in the surroundings of HFLS3. We use the Millennium Simulation to illustrate that HFLS3 may be expected to have companions if it is as massive as claimed, but find no significant evidence from the surface density of SCUBA-2 galaxies in its vicinity, or their colors, that HFLS3 marks an over-density of dusty, star-forming galaxies. We cannot rule out the presence of dusty neighbours with confidence, but deeper 450-um imaging has the potential to more tightly constrain the redshifts of nearby galaxies, at least one of which likely lies at z>~5. If associations with HFLS3 can be ruled out, this could be taken as evidence that HFLS3 is less biased than a simple extrapolation of the Millennium Simulation may imply. This could suggest either that it represents a rare short-lived, but highly luminous, phase in the evolution of an otherwise typical galaxy, or that this system has suffered amplification due to a foreground gravitational lens and so is not as intrinsically luminous as claimed.

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arXiv2014

[CII] and 12CO(1-0) Emission Maps in HLSJ091828.6+514223: A Strongly Lensed Interacting System at z=5.24

We present Submillimeter Array (SMA) [CII] 158um and Jansky Very Large Array (JVLA) $^{12}$CO(1-0) line emission maps for the bright, lensed, submillimeter source at $z=5.2430$ behind Abell 773: HLSJ091828.6+514223 (HLS0918). We combine these measurements with previously reported line profiles, including multiple $^{12}$CO rotational transitions, [CI], water and [NII], providing some of the best constraints on the properties of the interstellar medium (ISM) in a galaxy at $z>5$. HLS0918 has a total far-infrared (FIR) luminosity L_FIR(8-1000um) = (1.6$\pm$0.1)x10^14 L_sun/mu, where the total magnification mu_total = 8.9$\pm$1.9, via a new lens model from the [CII] and continuum maps. Despite a HyLIRG luminosity, the FIR continuum shape resembles that of a local LIRG. We simultaneously fit all of the observed spectral line profiles, finding four components which correspond cleanly to discrete spatial structures identified in the maps. The two most redshifted spectral components occupy the nucleus of a massive galaxy, with a source plane separation <1 kpc. The reddest dominates the continuum map (de-magnified L_FIR = (1.1$\pm$0.2)x10^13 L_sun), and excites strong water emission in both nuclear components via a powerful FIR radiation field from the intense star formation. A third star-forming component is most likely a region of a merging companion (dV ~ 500 km/s) exhibiting generally similar gas properties. The bluest component originates from a spatially distinct region, and photo-dissociation region (PDR) analysis suggests that it is lower density, cooler and forming stars less vigorously than the other components. Strikingly, it has very strong [NII] emission which may suggest an ionized, molecular outflow. This comprehensive view of gas properties and morphology in HLS0918 previews the science possible for a large sample of high-redshift galaxies once ALMA attains full sensitivity.

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arXiv2013

Herschel-ATLAS: deep HST/WFC3 imaging of strongly lensed submillimeter galaxies

We report on deep near-infrared observations obtained with the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope (HST) of the first five confirmed gravitational lensing events discovered by the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS). We succeed in disentangling the background galaxy from the lens to gain separate photometry of the two components. The HST data allow us to significantly improve on previous constraints of the mass in stars of the lensed galaxy and to perform accurate lens modelling of these systems, as described in the accompanying paper by Dye et al. We fit the spectral energy distributions of the background sources from near-IR to millimetre wavelengths and use the magnification factors estimated by Dye et al. to derive the intrinsic properties of the lensed galaxies. We find these galaxies to have star-formation rates of approximately 400 to 2000 M_sol/yr, with approximately (6-25)x10^10 M_sol of their baryonic mass already turned into stars. At these rates of star formation, all remaining molecular gas will be exhausted in less than 100 Myr, reaching a final mass in stars of a few 10^11 M_sol. These galaxies are thus proto-ellipticals caught during their major episode of star formation, and observed at the peak epoch z=1.5-3 of the cosmic star formation history of the Universe.

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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.

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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.

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arXiv2013

Gravitational Lens Models Based on Submillimeter Array Imaging of Herschel-selected Strongly Lensed Sub-millimeter Galaxies at z>1.5

Strong gravitational lenses are now being routinely discovered in wide-field surveys at (sub)millimeter wavelengths. We present Submillimeter Array (SMA) high-spatial resolution imaging and Gemini-South and Multiple Mirror Telescope optical spectroscopy of strong lens candidates discovered in the two widest extragalactic surveys conducted by the Herschel Space Observatory: the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS) and the Herschel Multi-tiered Extragalactic Survey (HerMES). From a sample of 30 Herschel sources with S_500>100 mJy, 21 are strongly lensed (multiply imaged), 4 are moderately lensed (singly imaged), and the remainder require additional data to determine their lensing status. We apply a visibility-plane lens modeling technique to the SMA data to recover information about the masses of the lenses as well as the intrinsic (i.e., unlensed) sizes (r_half) and far-infrared luminosities (L_FIR) of the lensed submillimeter galaxies (SMGs). The sample of lenses comprises primarily isolated massive galaxies, but includes some groups and clusters as well. Several of the lenses are located at z_lens>0.7, a redshift regime that is inaccessible to lens searches based on Sloan Digital Sky Survey spectroscopy. The lensed SMGs are amplified by factors that are significantly below statistical model predictions given the 500um flux densities of our sample. We speculate that this may reflect a deficiency in our understanding of the intrinsic sizes and luminosities of the brightest SMGs. The lensed SMGs span nearly one decade in L_FIR (median L_FIR=7.9x10^12 L_sun) and two decades in FIR luminosity surface density (median Sigma_FIR=6.0x10^11 L_sun kpc^-2). The strong lenses in this sample and others identified via (sub-)mm surveys will provide a wealth of information regarding the astrophysics of galaxy formation and evolution over a wide range in redshift.

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arXiv2013

An extended Herschel drop-out source in the center of AS1063, a 'normal' dusty galaxy at z=6.1 or SZ substructures?

In the course of our 870um APEX/LABOCA follow up of the Herschel Lensing Survey we have detected a source in AS1063 (RXC J2248.7-4431), that has no counterparts in any of the Herschel PACS/SPIRE bands, it is a Herschel 'drop-out' with S_870/S_500>0.5. The 870um emission is extended and centered on the brightest cluster galaxy suggesting either a multiply imaged background source or substructure in the Sunyaev-Zel'dovich (SZ) increment due to inhomogeneities in the hot cluster gas of this merging cluster. We discuss both interpretations with emphasis on the putative lensed source. Based on the observed properties and on our lens model we find that this source could be the first SMG with a moderate far infrared luminosity (L_FIR<10^12 L_sol) detected so far at z>4. In deep HST observations we identified a multiply imaged z~6 source and we measured its spectroscopic redshift z=6.107 with VLT/FORS. This source could be associated with the putative SMG but it is most likely offset spatially by 10-30kpc and they could be interacting galaxies. With a FIR luminosity in the range [5-15]x10^{11} L_sol corresponding to a star formation rate in the range [80-260]M_sol/yr, this SMG would be more representative than the extreme starbursts usually detected at z>4. With a total magnification of ~25 it would open a unique window to the 'normal' dusty galaxies at the end of the epoch of reionization.

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