arXiv subjects

P. van der Werf

Publications and source records attributed to P. van der Werf.

At least 127 records · Page 7Linked to original sources

arXiv2017

Recovering the properties of high redshift galaxies with different JWST broad-band filters

Imaging with the James Webb Space Telescope (JWST) will allow for observing the bulk of distant galaxies at the epoch of reionisation. The recovery of their properties, such as age, color excess E(B-V), specific star formation rate (sSFR) and stellar mass, will mostly rely on spectral energy distribution fitting, based on the data provided by JWST's two imager cameras, namely the Near Infrared Camera (NIRCam) and the Mid Infrared Imager (MIRI). In this work we analyze the effect of choosing different combinations of NIRCam and MIRI broad-band filters, from 0.6 μm to 7.7 μm, on the recovery of these galaxy properties. We performed our tests on a sample of 1542 simulated galaxies, with known input properties, at z=7-10. We found that, with only 8 NIRCam broad-bands, we can recover the galaxy age within 0.1 Gyr and the color excess within 0.06 mag for 70% of the galaxies. Besides, the stellar masses and sSFR are recovered within 0.2 and 0.3 dex, respectively, at z=7-9. Instead, at z=10, no NIRCam band traces purely the λ> 4000 Å regime and the percentage of outliers in stellar mass (sSFR) increases by > 20% (> 90%), in comparison to z=9. The MIRI F560W and F770W bands are crucial to improve the stellar mass and the sSFR estimation at z=10. When nebular emission lines are present, deriving correct galaxy properties is challenging, at any redshift and with any band combination. In particular, the stellar mass is systematically overestimated in up to 0.3 dex on average with NIRCam data alone and including MIRI observations improves only marginally the estimation.

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arXiv2017

VALES: I. The molecular gas content in star-forming dusty H-ATLAS galaxies up to z=0.35

We present an extragalactic survey using observations from the Atacama Large Millimeter/submillimeter Array (ALMA) to characterise galaxy populations up to $z=0.35$: the Valparaíso ALMA Line Emission Survey (VALES). We use ALMA Band-3 CO(1--0) observations to study the molecular gas content in a sample of 67 dusty normal star-forming galaxies selected from the $Herschel$ Astrophysical Terahertz Large Area Survey ($H$-ATLAS). We have spectrally detected 49 galaxies at $>5σ$ significance and 12 others are seen at low significance in stacked spectra. CO luminosities are in the range of $(0.03-1.31)\times10^{10}$ K km s$^{-1}$ pc$^2$, equivalent to $\log({\rm M_{gas}/M_{\odot}}) =8.9-10.9$ assuming an $α_{\rm CO}$=4.6(K km s$^{-1}$ pc$^{2}$)$^{-1}$, which perfectly complements the parameter space previously explored with local and high-z normal galaxies. We compute the optical to CO size ratio for 21 galaxies resolved by ALMA at $\sim 3$."$5$ resolution (6.5 kpc), finding that the molecular gas is on average $\sim$ 0.6 times more compact than the stellar component. We obtain a global Schmidt-Kennicutt relation, given by $\log [Σ_{\rm SFR}/({\rm M_{\odot} yr^{-1}kpc^{-2}})]=(1.26 \pm 0.02) \times \log [Σ_{\rm M_{H2}}/({\rm M_{\odot}\,pc^{-2}})]-(3.6 \pm 0.2)$. We find a significant fraction of galaxies lying at `intermediate efficiencies' between a long-standing mode of star-formation activity and a starburst, specially at $\rm L_{IR}=10^{11-12} L_{\odot}$. Combining our observations with data taken from the literature, we propose that star formation efficiencies can be parameterised by $\log [{\rm SFR/M_{H2}}]=0.19 \times {\rm (\log {L_{IR}}-11.45)}-8.26-0.41 \times \arctan[-4.84 (\log {\rm L_{IR}}-11.45) ]$. Within the redshift range we explore ($z<0.35$), we identify a rapid increase of the gas content as a function of redshift.

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arXiv2017

VALES: III. The calibration between the dust continuum and interstellar gas content of star-forming galaxies

We present the calibration between the dust continuum luminosity and interstellar gas content obtained from the Valparaíso ALMA Line Emission Survey (VALES) sample of 67 main-sequence star-forming galaxies at 0.02<$z$<0.35. We use CO(1-0) observations from the Atacama Large Millimetre/submillimetre Array (ALMA) to trace the molecular gas mass, $M_{\mathrm{H}_{2}}$, and estimate the rest-frame monochromatic luminosity at 850 $μ$m, $L_{ν_{850}}$, by extrapolating the dust continuum from MAGPHYS modelling of the far-ultraviolet to submillimetre spectral energy distribution sampled by the Galaxy And Mass Assembly (GAMA) survey. Adopting $α_{\rm CO}$ = 6.5 (K km s$^{-1}$ pc$^{2}$)$^{-1}$, the average ratio of $L_{ν_{850}}/M_{\mathrm{H}_{2}}$ = (6.4$\pm$1.4)$\times10^{19}$ erg s$^{-1}$ Hz$^{-1}$ $\mathrm{M}_{\odot}^{-1}$, in excellent agreement with literature values. We obtain a linear fit of $\log_{10}$ ($M_{\mathrm{H}_{2}}/\mathrm{M}_{\odot}$) = (0.92$\pm$0.02) $\log_{10}$ ($L_{ν_{850}}$/erg s$^{-1}$ Hz$^{-1}$)-(17.31$\pm$0.59). We provide relations between $L_{ν_{850}}$, $M_{\mathrm{H}_{2}}$ and $M_{\mathrm{ISM}}$ when combining the VALES and literature samples, and adopting a Galactic $α_{\rm CO}$ value.

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arXiv2017

Luminous, pc-scale CO 6-5 emission in the obscured nucleus of NGC1377

High resolution submm observations are important in probing the morphology, column density and dynamics of obscured active galactic nuclei (AGNs). With high resolution (0.06 x 0.05) ALMA 690 GHz observations we have found bright (TB >80 K) and compact (FWHM 10x7 pc) CO 6-5 line emission in the nucleus of the extremely radio-quiet galaxy NGC1377. The integrated CO 6-5 intensity is aligned with the previously discovered jet/outflow of NGC1377 and is tracing the dense (n>1e4 cm-3), hot gas at the base of the outflow. The velocity structure is complex and shifts across the jet/outflow are discussed in terms of jet-rotation or separate, overlapping kinematical components. High velocity gas (deltaV +-145 km/s) is detected inside r<2-3 pc and we suggest that it is emerging from an inclined rotating disk or torus of position angle PA=140+-20 deg with a dynamical mass of approx 3e6 Msun. This mass is consistent with that of a supermassive black hole (SMBH), as inferred from the M-sigma relation. The gas mass of the proposed disk/torus constitutes <3% of the nuclear dynamical mass. In contrast to the intense CO 6-5 line emission, we do not detect dust continuum with an upper limit of S(690GHz)<2mJy. The corresponding, 5 pc, H2 column density is estimated to N(H2)<3e23 cm-2, which is inconsistent with a Compton Thick (CT) source. We discuss the possibility that CT obscuration may be occuring on small (subparsec) or larger scales. From SED fitting we suggest that half of the IR emission of NGC1377 is nuclear and the rest (mostly the far-infrared (FIR)) is more extended. The extreme radio quietness, and the lack of emission from other star formation tracers, raise questions on the origin of the FIR emission. We discuss the possibility that it is arising from the dissipation of shocks in the molecular jet/outflow or from irradiation by the nuclear source along the poles.

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arXiv2017

The AT-LESS CO(1-0) survey of submillimetre galaxies in the Extended Chandra Deep Field South: First results on cold molecular gas in galaxies at z ~ 2

We present the first results from our on-going Australia Telescope Compact Array survey of CO(1-0) in ALMA-identified submillimetre galaxies in the Extended Chandra Deep Field South. Strong detections of CO(1-0) emission from two submillimetre galaxies, ALESS 122.1 (z = 2.0232) and ALESS 67.1 (z = 2.1230), were obtained. We estimate gas masses of M_gas ~ 1.3 \times 10^{11} M_odot and M_gas ~ 1.0 \times 10^{11} M_\odot for ALESS 122.1 and ALESS 67.1, respectively, adopting alpha_CO = 1.0. Dynamical mass estimates from the kinematics of the CO(1-0) line yields M_dyn (sin i)^2 = 2.1 +- 1.1 \times 10^{11} M_odot and (3.2 +- 0.9) \times 10^{11} M_\odot for ALESS 122.1 and ALESS 67.1, respectively. This is consistent with the total baryonic mass estimates of these two systems. We examine star formation efficiency using the L_FIR versus L'_CO(1-0) relation for samples of local ULIRGs and LIRGs, and more distant star-forming galaxies, with CO(1-0) detections. We find some evidence of a shallower slope for ULIRGs and SMGs compared to less luminous systems, but a larger sample is required for definite conclusions. We determine gas-to-dust ratios of 170 +- 30 and 140 +- 30 for ALESS 122.1 and ALESS 67.1, respectively, showing ALESS 122.1 has an unusually large gas reservoir. By combining the 38.1 GHz continuum detection of ALESS 122.1 with 1.4 and 5.5 GHz data, we estimate that the free-free contribution to radio emission at 38.1 GHz is 34 +- 17 microJy, yielding a star formation rate (1400 +- 700 M_\odot yr^{-1}) consistent with that from the infrared luminosity.

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arXiv2017

Evolution of cosmic star formation in the SCUBA-2 Cosmology Legacy Survey

We present a new exploration of the cosmic star-formation history and dust obscuration in massive galaxies at redshifts $0.5< z<6$. We utilize the deepest 450 and 850$μ$m imaging from SCUBA-2 CLS, covering 230arcmin$^2$ in the AEGIS, COSMOS and UDS fields, together with 100-250$μ$m imaging from Herschel. We demonstrate the capability of the T-PHOT deconfusion code to reach below the confusion limit, using multi-wavelength prior catalogues from CANDELS/3D-HST. By combining IR and UV data, we measure the relationship between total star-formation rate (SFR) and stellar mass up to $z\sim5$, indicating that UV-derived dust corrections underestimate the SFR in massive galaxies. We investigate the relationship between obscuration and the UV slope (the IRX-$β$ relation) in our sample, which is similar to that of low-redshift starburst galaxies, although it deviates at high stellar masses. Our data provide new measurements of the total SFR density (SFRD) in $M_\ast>10^{10}M_\odot$ galaxies at $0.5 10$. One third of this is accounted for by 450$μ$m-detected sources, while one fifth is attributed to UV-luminous sources (brighter than $L^\ast_{UV}$), although even these are largely obscured. By extrapolating our results to include all stellar masses, we estimate a total SFRD that is in good agreement with previous results from IR and UV data at $z\lesssim3$, and from UV-only data at $z\sim5$. The cosmic star-formation history undergoes a transition at $z\sim3-4$, as predominantly unobscured growth in the early Universe is overtaken by obscured star formation, driven by the build-up of the most massive galaxies during the peak of cosmic assembly.

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arXiv2016

The Dense Molecular Gas and Nuclear Activity in the ULIRG IRAS 13120-5453

We present new ALMA Band 7 ($\sim340$ GHz) observations of the dense gas tracers HCN, HCO$^+$, and CS in the local, single-nucleus, ultraluminous infrared galaxy IRAS 13120-5453. We find centrally enhanced HCN (4-3) emission, relative to HCO$^+$ (4-3), but do not find evidence for radiative pumping of HCN. Considering the size of the starburst (0.5 kpc) and the estimated supernovae rate of $\sim1.2$ yr$^{-1}$, the high HCN/HCO$^+$ ratio can be explained by an enhanced HCN abundance as a result of mechanical heating by the supernovae, though the active galactic nucleus and winds may also contribute additional mechanical heating. The starburst size implies a high $Σ_{IR}$ of $4.7\times10^{12}$ $L_{\odot}$ kpc$^{-2}$, slightly below predictions of radiation-pressure limited starbursts. The HCN line profile has low-level wings, which we tentatively interpret as evidence for outflowing dense molecular gas. However, the dense molecular outflow seen in the HCN line wings is unlikely to escape the galaxy and is destined to return to the nucleus and fuel future star formation. We also present modeling of Herschel observations of the H$_2$O lines and find a nuclear dust temperature of $\sim40$ K. IRAS 13120-5453 has a lower dust temperature and $Σ_{IR}$ than is inferred for the systems termed "compact obscured nuclei" (such as Arp 220 and Mrk 231). If IRAS 13120-5453 has undergone a compact obscured nucleus phase, we are likely witnessing it at a time when the feedback has already inflated the nuclear ISM and diluted star formation in the starburst/AGN core.

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arXiv2016

VALES: II. The physical conditions of interstellar gas in normal star-forming galaxies up to z=0.2 revealed by ALMA

We use new Band-3 CO(1-0) observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA) to study the physical conditions in the interstellar gas of a sample of 27 dusty main-sequence star-forming galaxies at 0.03<$z$<0.2 present in the Valparaíso ALMA Line Emission Survey (VALES). The sample is drawn from far-IR bright galaxies over $\sim$160 deg$^{2}$ in the Herschel Astrophysical Terahertz Large Area Survey (HATLAS), which is covered by Herschel [CII] 158 $μ$m spectroscopy and far-infrared (FIR) photometry. The [CII] and CO lines are both detected at >5$σ$ in 26 sources. We find an average [CII] to CO(1-0) luminosity ratio of 3500$\pm$1200 for our sample that is consistent with previous studies. Using the [CII], CO and FIR measurements as diagnostics of the physical conditions of the interstellar medium, we compare these observations to the predictions of a photodissociation region (PDR) model to determine the gas density, surface temperature, pressure, and the strength of the incident far-ultraviolet (FUV) radiation field, $G_{0}$, normalised to the Habing Field. The majority of our sample exhibit hydrogen densities of 4 < $\log n/\mathrm{cm}^{3}$ < 5.5 and experience an incident FUV radiation field with strengths of 2 < $\log G_0$ < 3 when adopting standard adjustments. A comparison to galaxy samples at different redshifts indicates that the average strength of the FUV radiation field appears constant up to redshift $z\sim$6.4, yet the neutral gas density increases with redshift by a factor of $\sim$100, that persists regardless of various adjustments to our observable quantities. This evolution could provide an explanation for the observed evolution of the star formation rate density with cosmic time, yet could arise from a combination of observational biases when using different suites of emission lines as diagnostic tracers of PDR gas.

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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

ATCA detections of massive molecular gas reservoirs in dusty, high-z radio galaxies

Observations using the 7 mm receiver system on the Australia Telescope Compact Array have revealed large reservoirs of molecular gas in two high-redshift radio galaxies: HATLAS J090426.9+015448 (z = 2.37) and HATLAS J140930.4+003803 (z = 2.04). Optically the targets are very faint, and spectroscopy classifies them as narrow-line radio galaxies. In addition to harbouring an active galactic nucleus the targets share many characteristics of sub-mm galaxies. Far-infrared data from Herschel-ATLAS suggest high levels of dust (>10^9 M_solar) and a correspondingly large amount of obscured star formation (~1000 M_solar / yr). The molecular gas is traced via the J = 1-0 transition of 12CO, its luminosity implying total H_2 masses of (1.7 +/- 0.3) x 10^11 and (9.5 +/- 2.4) x 10^10 (alpha_CO/0.8) M_solar in HATLAS J090426.9+015448 and HATLAS J140930.4+003803 respectively. Both galaxies exhibit molecular line emission over a broad (~1000 km/s) velocity range, and feature double-peaked profiles. We interpret this as evidence of either a large rotating disk or an on-going merger. Gas depletion timescales are ~100 Myr. The 1.4 GHz radio luminosities of our targets place them close to the break in the luminosity function. As such they represent `typical' z > 2 radio sources, responsible for the bulk of the energy emitted at radio wavelengths from accretion-powered sources at high redshift, and yet they rank amongst the most massive systems in terms of molecular gas and dust content. We also detect 115 GHz rest-frame continuum emission, indicating a very steep high-radio-frequency spectrum, possibly classifying the targets as compact steep spectrum objects.

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arXiv2016

VLA and ALMA Imaging of Intense, Galaxy-Wide Star Formation in z ~ 2 Galaxies

We present $\simeq$0$.\!\!^{\prime\prime}4$-resolution extinction-independent distributions of star formation and dust in 11 star-forming galaxies (SFGs) at $z = 1.3-3.0$. These galaxies are selected from sensitive, blank-field surveys of the $2' \times 2'$ Hubble Ultra-Deep Field at $λ= 5$ cm and 1.3 mm using the Karl G. Jansky Very Large Array (VLA) and Atacama Large Millimeter/submillimeter Array (ALMA). They have star-formation rates (SFRs), stellar masses, and dust properties representative of massive main-sequence SFGs at $z \sim 2$. Morphological classification performed on spatially-resolved stellar mass maps indicates a mixture of disk and morphologically disturbed systems; half of the sample harbor X-ray active galactic nuclei (AGN), thereby representing a diversity of $z \sim 2$ SFGs undergoing vigorous mass assembly. We find that their intense star formation most frequently occurs at the location of stellar-mass concentration and extends over an area comparable to their stellar-mass distribution, with a median diameter of $4.2 \pm 1.8$ kpc. This provides direct evidence for galaxy-wide star formation in distant, blank-field-selected main-sequence SFGs. The typical galactic-average SFR surface density is 2.5 M$_{\odot}$yr$^{-1}$kpc$^{-2}$, sufficiently high to drive outflows. In X-ray-selected AGN where radio emission is enhanced over the level associated with star formation, the radio excess pinpoints the AGN, which are found to be co-spatial with star formation. The median extinction-independent size of main-sequence SFGs is two times larger than those of bright submillimeter galaxies whose SFRs are $3-8$ times larger, providing a constraint on the characteristic SFR ($\sim300$ M$_{\odot}$yr$^{-1}$) above which a significant population of more compact star-forming galaxies appears to emerge.

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arXiv2016

The impact of JWST broad-band filter choice on photometric redshift estimation

The determination of galaxy redshifts in James Webb Space Telescope (JWST)'s blank-field surveys will mostly rely on photometric estimates, based on the data provided by JWST's Near-Infrared Camera (NIRCam) at 0.6-5.0 μm and Mid Infrared Instrument (MIRI) at λ>5.0 μm. In this work we analyse the impact of choosing different combinations of NIRCam and MIRI broad-band filters (F070W to F770W), as well as having ancillary data at λ<0.6 μm, on the derived photometric redshifts (zphot) of a total of 5921 real and simulated galaxies, with known input redshifts z=0-10. We found that observations at λ<0.6 μm are necessary to control the contamination of high-z samples by low-z interlopers. Adding MIRI (F560W and F770W) photometry to the NIRCam data mitigates the absence of ancillary observations at λ<0.6 μm and improves the redshift estimation. At z=7-10, accurate zphot can be obtained with the NIRCam broad bands alone when S/N>=10, but the zphot quality significantly degrades at S/N<=5. Adding MIRI photometry with one magnitude brighter depth than the NIRCam depth allows for a redshift recovery of 83-99%, depending on SED type, and its effect is particularly noteworthy for galaxies with nebular emission. The vast majority of NIRCam galaxies with [F150W]=29 AB mag at z=7-10 will be detected with MIRI at [F560W, F770W]<28 mag if these sources are at least mildly evolved or have spectra with emission lines boosting the mid-infrared fluxes.

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arXiv2016

The SCUBA-2 Cosmology Legacy Survey: The EGS deep field I - Deep number counts and the redshift distribution of the recovered Cosmic Infrared Background at 450 and 850 um

We present deep observations at 450 um and 850 um in the Extended Groth Strip field taken with the SCUBA-2 camera mounted on the James Clerk Maxwell Telescope as part of the deep SCUBA-2 Cosmology Legacy Survey (S2CLS), achieving a central instrumental depth of $σ_{450}=1.2$ mJy/beam and $σ_{850}=0.2$ mJy/beam. We detect 57 sources at 450 um and 90 at 850 um with S/N > 3.5 over ~70 sq. arcmin. From these detections we derive the number counts at flux densities $S_{450}>4.0$ mJy and $S_{850}>0.9$ mJy, which represent the deepest number counts at these wavelengths derived using directly extracted sources from only blank-field observations with a single-dish telescope. Our measurements smoothly connect the gap between previous shallower blank-field single-dish observations and deep interferometric ALMA results. We estimate the contribution of our SCUBA-2 detected galaxies to the cosmic infrared background (CIB), as well as the contribution of 24 um-selected galaxies through a stacking technique, which add a total of $0.26\pm0.03$ and $0.07\pm0.01$ MJy/sr, at 450 um and 850 um, respectively. These surface brightnesses correspond to $60\pm20$ and $50\pm20$ per cent of the total CIB measurements, where the errors are dominated by those of the total CIB. Using the photometric redshifts of the 24 um-selected sample and the redshift distributions of the submillimetre galaxies, we find that the redshift distribution of the recovered CIB is different at each wavelength, with a peak at $z\sim1$ for 450 um and at $z\sim2$ for 850um, consistent with previous observations and theoretical models.

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arXiv2016

Kiloparsec-scale dust disks in high-redshift luminous submillimeter galaxies

We present high-resolution (0.16$"$) 870um Atacama Large Millimeter/submillimeter Array (ALMA) imaging of 16 luminous (L_IR ~ 4 x 10^12 L_sun) submillimeter galaxies (SMGs) from the ALESS survey of the Extended Chandra Deep Field South. This dust imaging traces the dust-obscured star formation in these z~2.5 galaxies on ~1.3 kpc scales. The emission has a median effective radius of $R_e=0.24" \pm 0.02"$, corresponding to a typical physical size of $R_{e}=1.8\pm$0.2 kpc. We derive a median Sérsic index of $n=0.9\pm0.2$, implying that the dust emission is remarkably disk-like at the current resolution and sensitivity. We use different weighting schemes with the visibilities to search for clumps on 0.12$"$ (~1.0 kpc) scales, but we find no significant evidence for clumping in the majority of cases. Indeed, we demonstrate using simulations that the observed morphologies are generally consistent with smooth exponential disks, suggesting that caution should be exercised when identifying candidate clumps in even moderate S/N interferometric data. We compare our maps to comparable-resolution HST H$_{160}$-band images, finding that the stellar morphologies appear significantly more extended and disturbed, and suggesting that major mergers may be responsible for driving the formation of the compact dust disks we observe. The stark contrast between the obscured and unobscured morphologies may also have implications for SED fitting routines that assume the dust is co-located with the optical/near-IR continuum emission. Finally, we discuss the potential of the current bursts of star formation to transform the observed galaxy sizes and light profiles, showing that the $z\sim0$ descendants of these SMGs are expected to have stellar masses, effective radii, and gas surface densities consistent with the most compact massive (M_* ~ 1-2 x 10^11 M_sun) early-type galaxies observed locally.

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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

The molecular gas mass of M33

[Abridged] Do some environments favor efficient conversion of molecular gas into stars? To answer this, we need to be able to estimate the H2 mass. Traditionally, this is done using CO and a few assumptions but the Herschel observations in the FIR make it possible to estimate the molecular gas mass independently of CO. Previous attempts to derive gas masses from dust emission suffered from biases. Generally, dust surface densities, HI column densities, and CO intensities are used to derive a gas-to-dust ratio (GDR) and the local CO intensity to H2 column density ratio (XCO), sometimes allowing for an additional CO-dark gas component (Kdark). We tested earlier methods, revealing degeneracies among the parameters, and then used a Bayesian formalism to derive the most likely values for each of the parameters mentioned above as a function of position in the nearby low metallicity spiral galaxy M33. The data are from the IRAM 30m CO(2-1) line, high-resolution HI and Herschel dust continuum observations. Solving for GDR, XCO, and Kdark in macro pixels 500 pc in size, we find that (i) allowing for CO-dark gas significantly improves fits; (ii) Kdark decreases with galactocentric distance; (iii) GDR is slightly higher than initially expected and increases with galactocentric distance; (iv) the total amount of dark gas closely follows the radially decreasing CO emission, as might be expected if the dark gas is H2 where CO is photodissociated. The total amount of H2, including dark gas, yields an average XCO of twice the galactic value of 2e20 cm^-2/(K km/s), 55% of this traced directly through CO. The rather constant fraction of dark gas suggests that there is no large population of diffuse H2 clouds (unrelated to GMCs) without CO emission. Unlike in large spirals, we detect no systematic radial trend in XCO, possibly linked to the absence of a radial decrease in CO line ratios.

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arXiv2016

ALMA spectroscopic survey in the Hubble Ultra Deep Field: Continuum number counts, resolved 1.2-mm extragalactic background, and properties of the faintest dusty star forming galaxies

We present an analysis of a deep (1$σ$=13 $μ$Jy) cosmological 1.2-mm continuum map based on ASPECS, the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field. In the 1 arcmin$^2$ covered by ASPECS we detect nine sources at $>3.5σ$ significance at 1.2-mm. Our ALMA--selected sample has a median redshift of $z=1.6\pm0.4$, with only one galaxy detected at z$>$2 within the survey area. This value is significantly lower than that found in millimeter samples selected at a higher flux density cut-off and similar frequencies. Most galaxies have specific star formation rates similar to that of main sequence galaxies at the same epoch, and we find median values of stellar mass and star formation rates of $4.0\times10^{10}\ M_\odot$ and $\sim40~M_\odot$ yr$^{-1}$, respectively. Using the dust emission as a tracer for the ISM mass, we derive depletion times that are typically longer than 300 Myr, and we find molecular gas fractions ranging from $\sim$0.1 to 1.0. As noted by previous studies, these values are lower than using CO--based ISM estimates by a factor $\sim$2. The 1\,mm number counts (corrected for fidelity and completeness) are in agreement with previous studies that were typically restricted to brighter sources. With our individual detections only, we recover $55\pm4\%$ of the extragalactic background light (EBL) at 1.2 mm measured by the Planck satellite, and we recover $80\pm7\%$ of this EBL if we include the bright end of the number counts and additional detections from stacking. The stacked contribution is dominated by galaxies at $z\sim1-2$, with stellar masses of (1-3)$\times$10$^{10}$ M$_\odot$. For the first time, we are able to characterize the population of galaxies that dominate the EBL at 1.2 mm.

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