arXiv subjects

M. Aravena

Publications and source records attributed to M. Aravena.

At least 73 records · Page 4Linked to original sources

arXiv2021

MASCOT -- An ESO-ARO legacy survey of molecular gas in nearby SDSS-MaNGA galaxies: I. first data release, and global and resolved relations between H_2 and stellar content

We present the first data release of the MaNGA-ARO Survey of CO Targets (MASCOT), an ESO Public Spectroscopic Survey conducted at the Arizona Radio Observatory (ARO). We measure the CO(1-0) line emission in a sample of 187 nearby galaxies selected from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey that has obtained integral field unit (IFU) spectroscopy for a sample of ~ 10,000 galaxies at low redshift. The main goal of MASCOT is to probe the molecular gas content of star-forming galaxies with stellar masses > 10^9.5 M_solar and with associated MaNGA IFU observations and well-constrained quantities like stellar masses, star formation rates and metallicities. In this paper we present the first results of the MASCOT survey, providing integrated CO(1-0) measurements that cover several effective radii of the galaxy and present CO luminosities, CO kinematics, and estimated H2 gas masses. We observe that the decline of galaxy star formation rate with respect to the star formation main sequence (SFMS) increases with the decrease of molecular gas and with a reduced star formation efficiency, in agreement with results of other integrated studies. Relating the molecular gas mass fractions with the slope of the stellar age gradients inferred from the MaNGA observations, we find that galaxies with lower molecular gas mass fractions tend to show older stellar populations close to the galactic center, while the opposite is true for galaxies with higher molecular gas mass fractions, providing tentative evidence for inside-out quenching.

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arXiv2021

CONCERTO at APEX: Installation and first phase of on-sky commissioning

CONCERTO (CarbON CII line in post-rEionisation and ReionisaTiOn) is a large field-of-view (FoV) spectro-imager that has been installed on the Cassegrain Cabin of Atacama Pathfinder EXperiment (APEX) telescope in April 2021. CONCERTO hosts 2 focal planes and a total number of 4000 Kinetic Inductance Detectors (KID), with an instantaneous FoV of 18.6 arcminutes in the range of 130-310 GHz. The spectral resolution can be easily tuned down to 1 GHz depending on the scientific target. The scientific program of CONCERTO has many objectives, with two main programs focused on mapping the fluctuations of the [CII] line intensity in the reionisation and post-reionisation epoch (4.5<z<8.5), and on studying galaxy clusters via the thermal and kinetic Sunyaev-Zel'dovich (SZ) effect. CONCERTO will also measure the dust and molecular gas contents of local and intermediate-redshift galaxies, it will study the Galactic star-forming clouds and finally it will observe the CO intensity fluctuations arising from 0.3<z<2 galaxies. The design of the instrument, installation at APEX and current status of the commissioning phase and science verification will be presented. Also we describe the deployment and first on-sky tests performed between April and June 2021.

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arXiv2021

Normal, Dust-Obscured Galaxies in the Epoch of Reionization

Over the past decades, rest-frame ultraviolet (UV) observations have provided large samples of UV luminous galaxies at redshift (z) greater than 6, during the so-called epoch of reionization. While a few of these UV identified galaxies revealed significant dust reservoirs, very heavily dust-obscured sources at these early times have remained elusive. They are limited to a rare population of extreme starburst galaxies, and companions of rare quasars. These studies conclude that the contribution of dust-obscured galaxies to the cosmic star formation rate density at $z>6$ is sub-dominant. Recent ALMA and Spitzer observations have identified a more abundant, less extreme population of obscured galaxies at $z=3-6$. However, this population has not been confirmed in the reionization epoch so far. Here, we report the discovery of two dust-obscured star forming galaxies at $z=6.6813\pm0.0005$ and $z=7.3521\pm0.0005$. These objects are not detected in existing rest-frame UV data, and were only discovered through their far-infrared [CII] lines and dust continuum emission as companions to typical UV-luminous galaxies at the same redshift. The two galaxies exhibit lower infrared luminosities and star-formation rates than extreme starbursts, in line with typical star-forming galaxies at $z\sim7$. This population of heavily dust-obscured galaxies appears to contribute 10-25 per cent to the $z>6$ cosmic star formation rate density.

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arXiv2021

Molecular gas budget and characterization of intermediate-mass star-forming galaxies at $z\approx 2-3$

Star-forming galaxies (SFGs) with stellar masses below $10^{10}\,M_\odot$ make up the bulk of the galaxy population at $z>2$. The properties of the cold gas in these galaxies can only be probed in very deep ALMA observations or by targeting strongly lensed galaxies. Here we report the results of a pilot survey using the Atacama Compact Array (ACA) of molecular gas in the most strongly magnified galaxies selected as giant arcs in optical data. The selection in rest-frame UV wavelengths ensures that sources are regular star forming galaxies, without a priori indications of intense dusty starburst activity. We conducted Band 4 and Band 7 observations to detect mid-$J$ CO, [C I] and thermal continuum as molecular gas tracers from four strongly lensed systems at $z\approx2-3$: our targets are SGAS J1226651.3+215220 (A and B), SGAS J003341.5+024217 and the Sunburst Arc. The measured molecular mass is then projected onto the source plane with detailed lens models developed from high resolution HST observations. Multiwavelength photometry is then used to obtain the intrinsic stellar mass and star formation rate via SED fitting. In only one of the sources are the three tracers robustly detected, while in the others they are either undetected or detected in continuum only. The implied molecular gass masses range from $4\times 10^{9}\,M_\odot$ in the detected source to an upper limit of $\lesssim 10^9\,M_\odot$ in the most magnified source. The inferred gas fraction and gas depletion timescale are found to lie approximately 0.5 to 1.0 dex below the established scaling relations based on previous studies of unlensed massive galaxies. Our results indicate that the cold gas content of intermediate to low mass galaxies should not be extrapolated from the trends seen in more massive high-$z$ galaxies. (Abridged abstract)

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arXiv2021

Ultra-faint [CII] emission in a redshift = 2 gravitationally-lensed metal-poor dwarf galaxy

Extreme emission-line galaxies (EELGs) at redshift z=1-2 provide a unique view of metal-poor, starburst sources that are the likely drivers of the cosmic reionization at z$\geq6$. However, the molecular gas reservoirs of EELGs - the fuel for their intense star-formation - remain beyond the reach of current facilities. We present ALMA [CII] and PdBI CO(2-1) observations of a z=1.8, strongly lensed EELG SL2S 0217, a bright Lyman-$α$ emitter with a metallicity 0.05 $Z_\odot$. We obtain a tentative (3-4$σ$) detection of the [CII] line and set an upper limit on the [CII]/SFR ratio of $\leq1\times10^6$ $L_\odot$/($M_\odot$ yr$^{-1}$), based on the synthesized images and visibility-plane analysis. The CO(2-1) emission is not detected. Photoionization modelling indicates that up to 80% of the [CII] emission originates from neutral or molecular gas, although we can not rule out that the gas is fully ionized. The very faint [CII] emission is in line with both nearby metal-poor dwarfs and high-redshift Lyman-$α$ emitters, and predictions from hydrodynamical simulations. However, the [CII] line is 30$\times$ fainter than predicted by the De Looze et al. [CII]-SFR relation for local dwarfs, illustrating the danger of extrapolating locally-calibrated relations to high-redshift, metal-poor galaxies.

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arXiv2021

The infrared-radio correlation of star-forming galaxies is strongly M$_{\star}$-dependent but nearly redshift-invariant since z$\sim$4

Several works in the past decade have used the ratio between total (rest 8-1000$μ$m) infrared and radio (rest 1.4~GHz) luminosity in star-forming galaxies (q$_{IR}$), often referred to as the "infrared-radio correlation" (IRRC), to calibrate radio emission as a star formation rate (SFR) indicator. Previous studies constrained the evolution of q$_{IR}$ with redshift, finding a mild but significant decline, that is yet to be understood. For the first time, we calibrate q$_{IR}$ as a function of \textit{both} stellar mass (M$_{\star}$) and redshift, starting from an M$_{\star}$-selected sample of $>$400,000 star-forming galaxies in the COSMOS field, identified via (NUV-r)/(r-J) colours, at redshifts 0.1$<$z$<$4.5. Within each (M$_{\star}$,z) bin, we stack the deepest available infrared/sub-mm and radio images. We fit the stacked IR spectral energy distributions with typical star-forming galaxy and IR-AGN templates, and carefully remove radio AGN candidates via a recursive approach. We find that the IRRC evolves primarily with M$_{\star}$, with more massive galaxies displaying systematically lower q$_{IR}$. A secondary, weaker dependence on redshift is also observed. The best-fit analytical expression is the following: q$_{IR}$(M$_{\star}$,z)=(2.646$\pm$0.024)$\times$(1+z)$^{(-0.023\pm0.008)}$-(0.148$\pm$0.013)$\times$($\log~M_{\star}$/M$_{\odot}$-10). The lower IR/radio ratios seen in more massive galaxies are well described by their higher observed SFR surface densities. Our findings highlight that using radio-synchrotron emission as a proxy for SFR requires novel M$_{\star}$-dependent recipes, that will enable us to convert detections from future ultra deep radio surveys into accurate SFR measurements down to low-SFR, low-M$_{\star}$ galaxies.

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arXiv2021

Optical and near-infrared observations of the SPT2349-56 proto-cluster core at z = 4.3

We present Gemini-S and {\it Spitzer}-IRAC optical-through-near-IR observations in the field of the SPT2349-56 proto-cluster at $z=4.3$. We detect optical/IR counterparts for only nine of the 14 submillimetre galaxies (SMGs) previously identified by ALMA in the core of SPT2349-56. In addition, we detect four $z\sim4$ Lyman-break galaxies (LBGs) in the 30 arcsec diameter region surrounding this proto-cluster core. Three of the four LBGs are new systems, while one appears to be a counterpart of one of the nine observed SMGs. We identify a candidate brightest cluster galaxy (BCG) with a stellar mass of $(3.2^{+2.5}_{-1.4})\times10^{11}\,{\rm M}_{\odot}$. The stellar masses of the eight other SMGs place them on, above, and below the main sequence of star formation at $z\approx4.5$. The cumulative stellar mass for the SPT2349-56 core is at least $(11.5\pm2.9)\times10^{11}\,{\rm M}_{\odot}$, a sizeable fraction of the stellar mass in local BCGs, and close to the universal baryon fraction (0.16) relative to the virial mass of the core ($10^{13}\,{\rm M}_{\odot}$). As all 14 of these SMGs are destined to quickly merge, we conclude that the proto-cluster core has already developed a significant stellar mass at this early stage, comparable to $z=1$ BCGs. Importantly, we also find that the SPT2349-56 core structure would be difficult to uncover in optical surveys, with none of the ALMA sources being easily identifiable or constrained through $g,r,$ and $i$ colour-selection in deep optical surveys and only a modest overdensity of LBGs over the extended core structure. SPT2349-56 therefore represents a truly dust-obscured phase of a massive cluster core under formation.

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arXiv2021

The Evolution of the IR Luminosity Function and Dust-obscured Star Formation in the Last 13 Billion Years

We present the first results from the 2mm Mapping Obscuration to Reionization (MORA) survey, the largest ALMA contiguous blank-field survey to-date with a total area of 184 sq. arcmin and the only at 2mm to search for dusty star-forming galaxies (DSFGs). We use the 13 sources detected above 5sigma to estimate the first ALMA galaxy number counts at this wavelength. These number counts are then combined with the state-of-the-art galaxy number counts at 1.2mm and 3mm and with a backward evolution model to place constraints on the evolution of the IR luminosity function and dust-obscured star formation in the last 13 billion years. Our results suggest a steep redshift evolution on the space density of DSFGs and confirm the flattening of the IR luminosity function at faint luminosities, with a slope of $α_{LF} = -0.42^{+0.02}_{-0.04}$. We conclude that the dust-obscured component, which peaks at z=2-2.5, has dominated the cosmic history of star formation for the past ~12 billion years, back to z~4. At z=5, the dust-obscured star formation is estimated to be ~35% of the total star formation rate density and decreases to 25%-20% at z=6-7, implying a minor contribution of dust-enshrouded star formation in the first billion years of the Universe. With the dust-obscured star formation history constrained up to the end of the epoch of reionization, our results provide a benchmark to test galaxy formation models, to study the galaxy mass assembly history, and to understand the dust and metal enrichment of the Universe at early times.

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arXiv2021

Environments of a sample of AzTEC submillimetre galaxies in the COSMOS field

Submillimetre galaxies (SMGs) are bright sources at submillimetre wavelengths. Made up of mostly of high-z galaxies, SMGs are amongst the most luminous dusty galaxies in the Universe. Studying their environments and clustering strength is thus important to put these galaxies in a cosmological context. We present an environmental study of a sample of 116 SMGs in 96 ALMA observation fields, which were initially discovered with the AzTEC camera on ASTE and identified with high-resolution ALMA imaging within the COSMOS survey field, having either spectroscopic or unambiguous photometric redshift. We analysed their environments making use of the latest release of the COSMOS photometric catalogue, COSMOS2015, a catalogue that contains precise photometric redshifts for more than half a million objects over the 2deg2 COSMOS field. We searched for dense galaxy environments computing the so-called overdensity parameter as a function of distance within a radius of 5 arcmin from the SMG. We validated this approach spectroscopically for those SMGs for which spectroscopic redshift is available. As an additional test, we searched for extended X-ray emission as a proxy for the hot intracluster medium, performing an X-ray stacking analysis in the 0.5-2 keV band with a 32 arcsec aperture and our SMG position using all available XMM-Newton and Chandra X-ray observations of the COSMOS field. We find that 27% (31 out of 116) of the SMGs in our sample are located in a galactic dense environment; a fraction that is similar to previous studies. The spectroscopic redshift is known for 15 of these 31 sources, thus this photometric approach is tested using spectroscopy. We are able to confirm that 7 out of 15 SMGs lie in high-density peaks. However, the search for associated extended X-ray emission via an X-ray stacking analysis leads to a detection that is not statistically significant.

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arXiv2020

COLDz: Deep 34 GHz Continuum Observations and Free-free Emission in High-redshift Star-forming Galaxies

The high-frequency radio sky has historically remained largely unexplored due to the typical faintness of sources in this regime, and the modest survey speed compared to observations at lower frequencies. However, high-frequency radio surveys present an invaluable tracer of high-redshift star-formation, as they directly target the faint radio free-free emission. We present deep continuum observations at 34 GHz in the COSMOS and GOODS-North fields from the Karl G. Jansky Very Large Array (VLA), as part of the COLDz survey. The deep COSMOS mosaic spans $\sim10\text{arcmin}^2$ down to $σ=1.3μ\text{Jy beam}^{-1}$, while the wider GOODS-N observations cover $\sim50\text{arcmin}^2$ to $σ=5.3μ\text{Jy beam}^{-1}$. We present the deepest 34 GHz radio number counts to date, with five and thirteen continuum detections in COSMOS and GOODS-N, respectively. Nine galaxies show 34 GHz continuum emission that is originating from star-formation, although for two sources this is likely due to thermal emission from dust. Utilizing deep ancillary radio data at 1.4, 3, 5 and 10 GHz, we decompose the spectra of the remaining seven star-forming galaxies into their synchrotron and thermal free-free components, finding typical thermal fractions and synchrotron spectral indices comparable to those observed in local star-forming galaxies. Using calibrations from the literature, we determine free-free star-formation rates (SFRs), and show that these are in agreement with SFRs from spectral energy distribution fitting and the far-infrared/radio correlation. Our observations place strong direct constraints on the high-frequency radio emission in typical galaxies at high-redshift, and provide some of the first insight in what is set to become a key area of study with future radio facilities as the Square Kilometer Array Phase 1 and next-generation VLA.

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arXiv2020

The Complete Redshift Distribution of Dusty Star-forming Galaxies from the SPT-SZ Survey

The South Pole Telescope (SPT) has systematically identified 81 high-redshift, strongly gravitationally lensed, dusty star-forming galaxies (DSFGs) in a 2500 square degree cosmological mm-wave survey. We present the final spectroscopic redshift survey of this flux-limited ($S_{870\, \mathrm{μm}} > 25\, \mathrm{mJy}$) sample, initially selected at $1.4$ mm. The redshift survey was conducted with the Atacama Large Millimeter/submillimeter Array across the $3$ mm spectral window, targeting carbon monoxide line emission. By combining these measurements with ancillary data, the SPT sample is now spectroscopically complete, with redshifts spanning $1.9$$<$$z$$<$$6.9$ and a median of $z=3.9 \pm 0.2$. We present the mm through far-infrared photometry and spectral energy density fits for all sources, along with their inferred intrinsic properties. Comparing the properties of the SPT sources to the unlensed DSFG population, we demonstrate that the SPT-selected DSFGs represent the most extreme infrared-luminous galaxies, even after accounting for strong gravitational lensing. The SPT sources have a median star formation rate of $2.3(2)\times 10^3\, \mathrm{M_\odot yr^{-1}}$ and a median dust mass of $1.4(1)\times10^9\, \mathrm{M_\odot}$. However, the inferred gas depletion timescales of the SPT sources are comparable to those of unlensed DSFGs, once redshift is taken into account. This SPT sample contains roughly half of the known spectroscopically confirmed DSFGs at $z$$>$$5$, making this the largest sample of high-redshift DSFGs to-date, and enabling the "high-redshift tail" of extremely luminous DSFGs to be measured. Though galaxy formation models struggle to account for the SPT redshift distribution, the larger sample statistics from this complete and well-defined survey will help inform future theoretical efforts.

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arXiv2020

Observations of [OI]63micron line emission in main-sequence galaxies at z~1.5

We present Herschel-PACS spectroscopy of four main-sequence star-forming galaxies at z~1.5. We detect [OI]63micron line emission in BzK-21000 at z=1.5213, and measure a line luminosity, L([OI]63micron) = (3.9+/-0.7)x1.E+9 Lsun. Our PDR modelling of the interstellar medium in BzK-21000 suggests a UV radiation field strength, G~320 G0, and gas density, n~1800 cm-3, consistent with previous LVG modelling of the molecular CO line excitation. The other three targets in our sample are individually undetected in these data, and we perform a spectral stacking analysis which yields a detection of their average emission and an [OI]63micron line luminosity, L([OI]63micron) =(1.1+/-0.2)x1E+9 Lsun. We find that the implied luminosity ratio, L([OI]63micron)/L(IR), of the undetected BzK-selected star-forming galaxies broadly agrees with that of low-redshift star-forming galaxies, while BzK-21000 has a similar ratio to that of a dusty star-forming galaxy at z~6. The high [OI]63micron line luminosities observed in BzK-21000 and the $z \sim 1 -3$ dusty and submm luminous star-forming galaxies may be associated with extended reservoirs of low density, cool neutral gas.

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arXiv2020

A wide field-of-view low-resolution spectrometer at APEX: instrument design and science forecast

Characterise the large-scale structure in the Universe from present times to the high redshift epoch of reionisation is essential to constraining the cosmology, the history of star formation and reionisation, measuring the gas content of the Universe and obtaining a better understanding of the physical process that drive galaxy formation and evolution. Using the integrated emission from unresolved galaxies or gas clouds, line intensity mapping (LIM) provides a new observational window to measure the larger properties of structure. This very promising technique motivates the community to plan for LIM experiments. We describe the development of a large field-of-view instrument, named CONCERTO, operating in the range 130-310 GHz from the APEX 12-meters telescope. CONCERTO is a low-resolution spectrometer based on the Lumped Element Kinetic Inductance Detectors technology. Spectra are obtained using a fast Fourier Transform Spectrometer (FTS), coupled to a dilution cryostat with base temperature of 0.1K. Two 2 kilo-pixels arrays of LEKID are mounted inside the cryostat that also contains the cold optics and the front-end electronics. We present in detail the technological choices leading to the instrumental concept, together with the design and fabrication of the instrument and preliminary laboratory tests on the detectors. We also give our best estimates of CONCERTO sensitivity and give predictions for two of the main scientific goals of CONCERTO, i.e. a [CII]-intensity mapping survey and observations of galaxy clusters. We provide a detail description of the instrument design. Based on realistic comparisons with existing instruments developed by our group (NIKA, NIKA2, and KISS), and on laboratory detectors characterisation, we provide an estimate of CONCERTO sensitivity on sky. Finally, we describe in detail two out of the main science goals offered by CONCERTO at APEX.

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arXiv2020

VALES VI: ISM enrichment in star-forming galaxies up to z$\sim$0.2 using $^{12}$CO(1-0), $^{13}$CO(1-0) and C$^{18}$O(1-0) line luminosity ratios

We present Atacama Large Millimeter/sub-millimeter Array (ALMA) observations towards 27 low-redshift ($0.02< z<0.2$) star-forming galaxies taken from the Valparaíso ALMA/APEX Line Emission Survey (VALES). We perform stacking analyses of the $^{12}$CO($1-0$), $^{13}$CO($1-0$) and C$^{18}$O($1-0$) emission lines to explore the $L'$ ($^{12}$CO($1-0$))/$L'$($^{13}$CO($1-0$))) (hereafter $L'$($^{12}$CO)/$L'$($^{13}$CO)) and $L'$($^{13}$CO($1-0$))/$L'$(C$^{18}$O($1-0$)) (hereafter $L'$($^{13}$CO)/$L'$(C$^{18}$O) line luminosity ratio dependence as a function of different global galaxy parameters related to the star formation activity. The sample has far-IR luminosities $10^{10.1-11.9}$L$_{\odot}$ and stellar masses of $10^{9.8-10.9}$M$_{\odot}$ corresponding to typical star-forming and starburst galaxies at these redshifts. On average we find a $L'$($^{12}$CO)/$L'$($^{13}$CO) line luminosity ratio value of 16.1$\pm$2.5. Galaxies with evidences of possible merging activity tend to show higher $L'$($^{12}$CO)/$L'$($^{13}$CO) ratios by a factor of two, while variations of this order are also found in galaxy samples with higher star formation rates or star formation efficiencies. We also find an average $L'$($^{13}$CO)/$L'$(C$^{18}$O) line luminosity ratio of 2.5$\pm$0.6, which is in good agreement with those previously reported for starburst galaxies. We find that galaxy samples with high $L_{\text{IR}}$, SFR and SFE show low $L'$($^{13}$CO)/$L'$(C$^{18}$O) line luminosity ratios with high $L'$($^{12}$CO)/$L'$($^{13}$CO) line luminosity ratios, suggesting that these trends are produced by selective enrichment of massive stars in young starbursts.

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arXiv2020

Cold Molecular Gas and Free-Free Emission from Hot, Dust-Obscured Galaxies at $z$~3

We report on observations of redshifted CO(1-0) line emission and observed-frame $\rm\sim$ 30GHz radio continuum emission from five ultra-luminous, mid-IR selected hot, Dust-Obscured Galaxies (Hot DOGs) at $z\rm\gtrsim$ 3 using the Karl G. Jansky Very Large Array. We detect CO(1-0) line emission in all five Hot DOGs, with one of them at high signal to noise. We analyse FIR-radio spectral energy distributions, including dust, free-free and synchrotron emission for the galaxies. We find that most of the 115 GHz rest-frame continuum is mostly due to synchrotron or free-free emission, with only a potentially small contribution from thermal emission. We see a deficit in the rest-frame 115 GHz continuum emission compared to dusty star-forming galaxies (DSFGs) and sub-millimetre galaxies (SMGs) at high redshift, suggesting that Hot DOGs do not have similar cold gas reserves compared with star-forming galaxies. One target, W2305-0039, is detected in the FIRST 1.4 GHz survey, and is likely to possess compact radio jets. We compare to the FIR-radio correlation, and find that at least half of the Hot DOGs in our sample are radio-quiet with respect to normal galaxies. These findings suggest that Hot DOGs have comparably less cold molecular gas than star-forming galaxies at lower, $z\rm\sim$ 2 redshifts, and are dominated by powerful, yet radio-quiet AGN.

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arXiv2020

The [CII]/[NII] ratio in 3 < z < 6 sub-millimetre galaxies from the South Pole Telescope survey

We present Atacama Compact Array and Atacama Pathfinder Experiment observations of the [N II] 205 $μ$m fine-structure line in 40 sub-millimetre galaxies lying at redshifts z = 3 to 6, drawn from the 2500 deg$^2$ South Pole Telescope survey. This represents the largest uniformly selected sample of high-redshift [N II] 205 $μ$m measurements to date. 29 sources also have [C II] 158 $μ$m line observations allowing a characterization of the distribution of the [C II] to [N II] luminosity ratio for the first time at high-redshift. The sample exhibits a median L$_{[C II]}$ /L$_{[N II]}$ $\approx$ 11 and interquartile range of 5.0 to 24.7. These ratios are similar to those observed in local (U)LIRGs, possibly indicating similarities in their interstellar medium. At the extremes, we find individual sub-millimetre galaxies with L$_{[C II]}$ /L$_{[N II]}$ low enough to suggest a smaller contribution from neutral gas than ionized gas to the [C II] flux and high enough to suggest strongly photon or X-ray region dominated flux. These results highlight a large range in this line luminosity ratio for sub-millimetre galaxies, which may be caused by variations in gas density, the relative abundances of carbon and nitrogen, ionization parameter, metallicity, and a variation in the fractional abundance of ionized and neutral interstellar medium.

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arXiv2020

Millimeter-wave Point Sources from the 2500-square-degree SPT-SZ Survey: Catalog and Population Statistics

We present a catalog of emissive point sources detected in the SPT-SZ survey, a contiguous 2530-square-degree area surveyed with the South Pole Telescope (SPT) from 2008 - 2011 in three bands centered at 95, 150, and 220 GHz. The catalog contains 4845 sources measured at a significance of 4.5 sigma or greater in at least one band, corresponding to detections above approximately 9.8, 5.8, and 20.4 mJy in 95, 150, and 220 GHz, respectively. Spectral behavior in the SPT bands is used for source classification into two populations based on the underlying physical mechanisms of compact, emissive sources that are bright at millimeter wavelengths: synchrotron radiation from active galactic nuclei and thermal emission from dust. The latter population includes a component of high-redshift sources often referred to as submillimeter galaxies (SMGs). In the relatively bright flux ranges probed by the survey, these sources are expected to be magnified by strong gravitational lensing. The survey also contains sources consistent with protoclusters, groups of dusty galaxies at high redshift undergoing collapse. We cross-match the SPT-SZ catalog with external catalogs at radio, infrared, and X-ray wavelengths and identify available redshift information. The catalog splits into 3980 synchrotron-dominated and 865 dust-dominated sources and we determine a list of 506 SMGs. Ten sources in the catalog are identified as stars. We calculate number counts for the full catalog, and synchrotron and dusty components, using a bootstrap method and compare our measured counts with models. This paper represents the third and final catalog of point sources in the SPT-SZ survey.

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arXiv2020

A hyper luminous starburst at z=4.72 magnified by a lensing galaxy pair at z=1.48

[Abridged] We discovered in the Herschel Reference Survey an extremely bright IR source with $S_{500}$~120mJy (Red Virgo 4 - RV4). Based on IRAM/EMIR and IRAM/NOEMA detections of the CO(5-4), CO(4-3), and [CI] lines, RV4 is located at z=4.724, yielding a total observed L$_{IR}$ of 1.1+/-0.6x0$^{14}$L$_{\odot}$. At the position of the Herschel emission, three blobs are detected with the VLA at 10cm. The CO(5-4) line detection of each blob confirms that they are at the same redshift with the same line width, indicating that they are multiple images of the same source. In Spitzer and deep optical observations, two sources, High-z Lens 1 (HL1) West and HL1 East, are detected at the center of the three VLA/NOEMA blobs. These two sources are placed at z=1.48 with XSHOOTER spectra, suggesting that they could be merging and gravitationally lensing the emission of RV4. HL1 is the second most distant lens known to date in strong lensing systems. The Einstein radius of the lensing system is 2.2"+/-0.2 (20kpc). The high redshift of HL1 and the large Einstein radius are highly unusual for a strong lensing system. We present the ISM properties of the background source RV4. Different estimates of the gas depletion time yield low values suggesting that RV4 is a SB galaxy. Among all high-z SMGs, this source exhibits one of the lowest L$_{[CI]}$ to L$_{IR}$ ratios, 3.2+/-0.9x10$^{-6}$, suggesting an extremely short gas tdepl of only 14+/-5Myr. It also shows a relatively high L$_{[CI]}$ to L$_{CO(4-3)}$ ratio (0.7+/-0.2) and low L$_{CO(5-4)}$ to L$_{IR}$ ratio (only ~50% of the value expected for normal galaxies) hinting a low density of gas. Finally, we discuss that the short tdepl of RV4 can be explained by either a very high SFE, which is difficult to reconcile with major mergers simulations of high-z galaxies, or a rapid decrease of SF, which would bias the estimate of tdepl toward low value.

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