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J. Álvarez-Márquez

Publications and source records attributed to J. Álvarez-Márquez.

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arXiv2024

Clumpy star formation and an obscured nuclear starburst in the luminous dusty z=4 galaxy GN20 seen by MIRI/JWST

Dusty star-forming galaxies emit most of their light at far-IR to mm wavelengths as their star formation is highly obscured. Far-IR and mm observations have revealed their dust, neutral and molecular gas properties. The sensitivity of JWST at rest-frame optical and near-infrared wavelengths now allows the study of the stellar and ionized gas content. We investigate the spatially resolved distribution and kinematics of the ionized gas in GN20, a dusty star forming galaxy at $z$=4.0548. We present deep MIRI/MRS integral field spectroscopy of the near-infrared rest-frame emission of GN20. We detect spatially resolved \paa, out to a radius of 6 kpc, distributed in a clumpy morphology. The star formation rate derived from \paa\ (144 $\pm$ 9 \msunperyear) is only 7.7 $\pm 0.5 $\% of the infrared star formation rate (1860 $\pm$ 90 \msunperyear). We attribute this to very high extinction (A$_V$ = 17.2 $\pm$ 0.4 mag, or A$_{V,mixed}$ = 44 $\pm$ 3 mag), especially in the nucleus of GN20, where only faint \paa\ is detected, suggesting a deeply buried starburst. We identify four, spatially unresolved, clumps in the \paa\ emission. Based on the double peaked \paa\ profile we find that each clump consist of at least two sub-clumps. We find mass upper limits consistent with them being formed in a gravitationally unstable gaseous disk. The UV bright region of GN20 does not have any detected \paa\ emission, suggesting an age of more than 10 Myrs for this region of the galaxy. From the rotation profile of \paa\ we conclude that the gas kinematics are rotationally dominated and the $v_{rot}/σ_{m} = 3.8 \pm 1.4$ is similar to low-redshift LIRGs. We speculate that the clumps seen in GN20 could contribute to building up the inner disk and bulge of GN20.

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arXiv2024

High-precision astrometry and photometry with the JWST/MIRI imager

Astrometry is one of the main pillars of astronomy, and one of its oldest branches. Over the years, an increasing number of astrometric works by means of Hubble Space Telescope (HST) data have revolutionized our understanding of various phenomena. With the launch of JWST, it becomes almost instinctive to want to replicate or improve these results with data taken with the newest, state-of-the-art, space-based telescope. In this regard, the initial focus of the community has been on the Near-Infrared (NIR) detectors on board of JWST because of their high spatial resolution. This paper begins the effort to capture and apply what has been learned from HST to the Mid-InfraRed Instrument (MIRI) of JWST by developing the tools to obtain high-precision astrometry and photometry with its imager. We describe in detail how to create accurate effective point-spread-function (ePSF) models and geometric-distortion corrections, analyze their temporal stability, and test their quality to the extent of what is currently possible with the available data in the JWST MAST archive. We show that careful data reduction provides deep insight on the performance and intricacies of the MIRI imager, and of JWST in general. In an effort to help the community to devise new observing programs, we make our ePSF models and geometric-distortion corrections publicly available.

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arXiv2023

Geometric distortion and astrometric calibration of the JWST MIRI Medium Resolution Spectrometer

The Medium-Resolution integral field Spectrometer (MRS) of MIRI on board JWST performs spectroscopy between 5 and 28~$μ$m. The optics of the MRS introduce substantial distortion, and this needs to be rectified in order to reconstruct the observed astrophysical scene. We use data from the JWST/MIRI commissioning and cycle 1 calibration phase, to derive the MRS geometric distortion and astrometric solution, a critical step in the calibration of MRS data. These solutions come in the form of transform matrices that map the detector pixels to spatial coordinates of a local MRS coordinate system called $α$/$β$, to the global JWST observatory coordinates V2/V3. For every MRS spectral band and each slice dispersed on the detector, the transform of detector pixels to $α$/$β$ is fit by a two-dimensional polynomial, using a raster of point source observations. A polynomial transform is used to map the coordinates from $α$/$β$ to V2/V3. We calibrated the distortion of all 198 discrete slices of the MIRI/MRS IFUs, and derived an updated Field of View (FoV) for each MRS spectral band. The precision of the distortion solution is estimated to be better than one tenth of a spatial resolution element, with a root mean square (rms) of 10 milli-arcsecond (mas) at 5 $μ$m, to 23 mas at 27 $μ$m. Finally we find that the wheel positioning repeatability causes an additional astrometric error of rms 30 mas. We have demonstrated the MRS astrometric calibration strategy and analysis enabling the calibration of MRS spectra, a critical step in the data pipeline especially for science with spatially resolved objects. The distortion calibration was folded into the JWST pipeline in Calibration Reference Data System (CRDS) context jwst\_1094.pmap. The distortion calibration precision meets the pre-launch requirement, and the estimated total astrometric uncertainty is 50 mas.

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arXiv2023

Observations of the Planetary Nebula SMP LMC 058 with the JWST MIRI Medium Resolution Spectrometer

During the commissioning of {\em JWST}, the Medium-Resolution Spectrometer (MRS) on the Mid-Infrared Instrument (MIRI) observed the planetary nebula SMP LMC 058 in the Large Magellanic Cloud. The MRS was designed to provide medium resolution (R = $λ$/$Δλ$) 3D spectroscopy in the whole MIRI range. SMP LMC 058 is the only source observed in {\em JWST} commissioning that is both spatially and spectrally unresolved by the MRS and is a good test of {\em JWST's} capabilities. The new MRS spectra reveal a wealth of emission lines not previously detected in this planetary nebula. From these lines, the spectral resolving power ($λ$/$Δλ$) of the MRS is confirmed to be in the range R $=$ 4000 to 1500, depending on the MRS spectral sub-band. In addition, the spectra confirm that the carbon-rich dust emission is from SiC grains and that there is little to no time evolution of the SiC dust and emission line strengths over a 17-year epoch. These commissioning data reveal the great potential of the MIRI MRS for the study of circumstellar and interstellar material.

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arXiv2023

Uncovering the stellar structure of the dusty star-forming galaxy GN20 at z=4.055 with MIRI/JWST

Luminous infrared galaxies at high redshifts ($z$>4) include extreme starbursts that build their stellar mass over short periods of time (>100 Myr). These galaxies are considered to be the progenitors of massive quiescent galaxies at intermediate redshifts ($z\sim$2) but their stellar structure and buildup is unknown. Here, we present the first spatially resolved near-infrared imaging of GN20, one of the most luminous dusty star-forming galaxies known to date, observed at an epoch when the Universe was only 1.5 Gyr old. The 5.6$μ$m image taken with the JWST Mid-Infrared Instrument (MIRI/JWST) shows that GN20 is a very luminous galaxy (M$_\mathrm{1.1μm,AB}$=$-$25.01), with a stellar structure composed of a conspicuous central source and an extended envelope. The central source is an unresolved nucleus that carries 9% of the total flux. The nucleus is co-aligned with the peak of the cold dust emission, and offset by 3.9 kpc from the ultraviolet stellar emission. The diffuse stellar envelope is similar in size to the clumpy CO molecular gas distribution. The centroid of the stellar envelope is offset by 1 kpc from the unresolved nucleus, suggesting GN20 is involved in an interaction or merger event supported by its location as the brightest galaxy in a proto-cluster. The stellar size of GN20 is larger by a factor of about 3-5 than known spheroids, disks, and irregulars at $z\sim$4, while its size and low Sérsic index are similar to those measured in dusty, infrared luminous galaxies at $z\sim$2 of the same mass. GN20 has all the ingredients necessary for evolving into a massive spheroidal quiescent galaxy at intermediate $z$: it is a large, luminous galaxy at $z$=4.05 involved in a short and massive starburst centred in the stellar nucleus and extended over the entire galaxy, out to radii of 4 kpc, and likely induced by the interaction or merger with a member of the proto-cluster.

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arXiv2023

JWST MIRI/MRS in-flight absolute flux calibration and tailored fringe correction for unresolved sources

The MRS is one of the four observing modes of JWST/MIRI. Using JWST in-flight data of unresolved (point) sources, we can derive the MRS absolute spectral response function (ASRF) starting from raw data. Spectral fringing plays a critical role in the derivation and interpretation of the MRS ASRF. In this paper, we present an alternative way to calibrate the data. Firstly, we aim to derive a fringe correction that accounts for the dependence of the fringe properties on the MIRI pupil illumination and detector pixel sampling of the point spread function. Secondly, we aim to derive the MRS ASRF using an absolute flux calibrator observed across the full 5 to 28 $μ$m wavelength range of the MRS. Thirdly, we aim to apply the new ASRF to the spectrum of a G dwarf and compare with the output of the JWST/MIRI default data reduction pipeline. Finally, we examine the impact of the different fringe corrections on the detectability of molecular features in the G dwarf and K giant. The absolute flux calibrator HD 163466 (A-star) is used to derive tailored point source fringe flats at each of the default dither locations of the MRS. The fringe-corrected point source integrated spectrum of HD 163466 is used to derive the MRS ASRF using a theoretical model for the stellar continuum. A cross-correlation is run to quantify the uncertainty on the detection of CO, SiO, and OH in the K giant and CO in the G dwarf for different fringe corrections. The point-source-tailored fringe correction and ASRF are found to perform at the same level as the current corrections, beating down the fringe contrast to the sub-percent level, whilst mitigating the alteration of real molecular features. The same tailored solutions can be applied to other MRS unresolved targets. A pointing repeatability issue in the MRS limits the effectiveness of the tailored fringe flats is at short wavelengths.

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arXiv2023

Nuclear high-ionisation outflow in the Compton-thick AGN NGC6552 as seen by the JWST mid-infrared instrument

During the commissioning of the James Webb Space Telescope (JWST), the mid-infrared instrument (MIRI) observed NGC6552 with the MIRI Imager and the medium-resolution spectrograph (MRS). NGC6552 is an active galactic nucleus (AGN) at redshift 0.0266 classified as a Seyfert 2 nucleus in the optical, and Compton-thick AGN in X-rays. This work exemplifies and demonstrates the MRS capabilities to study the mid-infrared (mid-IR) spectra and characterize the physical conditions and kinematics of the ionized and molecular gas in the nuclear regions of nearby galaxies. We obtained the nuclear, circumnuclear, and central mid-IR spectra of NGC6552. They provide the first clear observational evidence for a nuclear outflow in NGC6552. The outflow contributes to 67$\pm$7% of the total line flux independent of the ionization potential (27 to 187 eV) and critical densities (10$^4$ to 4$\times$10$^{6}$ cm$^{-3}$), showing an average blue-shifted peak velocity of -127$\pm$45 kms$^{-1}$ and an outflow maximal velocity of 698$\pm$80 kms$^{-1}$. Since the mid-IR photons penetrate dusty regions as efficiently as X-ray keV photons, we interpret these results as the evidence for a highly ionized, non-stratified, AGN-powered, and fast outflowing gas in a low density environment (few 10$^{3}$ cm$^{-3}$) located very close (<0.2kpc) to the Compton-thick AGN. Nine pure rotational molecular Hydrogen lines are detected and spectrally resolved, and exhibit symmetric Gaussian profiles, consistent with the galactic rotation, and with no evidence of outflowing H$_{2}$ material. We detect a warm H$_{2}$ mass of $1.9\pm1.1\times10^7 M_{\odot}$ in the central region (1.8 kpc in diameter) of the galaxy, with almost 30% of that mass in the circum-nuclear region. Line ratios confirm that NGC6552 has a Seyfert nucleus with a black hole mass estimated in the range of 0.6 to 6 million solar masses.

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arXiv2023

MIRI/JWST observations reveal an extremely obscured starburst in the z=6.9 system SPT0311-58

Using MIRI on-board JWST we present mid-infrared sub-arcsec imaging (MIRIM) and spectroscopy (MRS) of the hyperluminous infrared system SPT0311-58 at z=6.9. MIRI observations are compared with existing ALMA far-infrared continuum and [CII]158$μ$m imaging. Even though the ALMA observations suggests very high star formation rates (SFR) in the eastern (E) and western (W) galaxies of the system, the H$α$ line is not detected. This, together with the detection of the Pa$α$ line, implies very high optical nebular extinction with lower limits of 4.2 (E) and 3.9 mag (W), and even larger 5.6 (E) and 10.0 (W) for SED derived values. The extinction-corrected Pa$α$ SFRs are 383 and 230M$_{\odot}$yr$^{-1}$ for the E and W galaxies, respectively. This represents 50% of the SFRs derived from the [CII]158$μ$m line and infrared light for the E galaxy and as low as 6% for the W galaxy. The MIRI observations reveal a clumpy stellar structure, with each clump having 3 to 5 $\times$10$^{9}$M$_\mathrm{\odot}$, leading to a total stellar mass of 2.0 and 1.5$\times$10$^{10}$M$_\mathrm{\odot}$ for the E and W galaxies, respectively. The specific SFR in the stellar clumps ranges from 25 to 59Gyr$^{-1}$, which are 3 to 10 times larger than the values measured in galaxies of similar mass at redshifts 6 to 8. The overall gas mass fraction is $M_\mathrm{gas}$/$M_*\sim3$, similar to that of z=4.5-6 star-forming galaxies. The observed properties of SPT0311-58 such as the clumpy distribution at sub(kpc) scales and the very high average extinction are similar to those observed in low- and intermediate-z LIRGs and ULIRGs, even though SPT0311-58 is observed only 800 Myr after the Big Bang. Massive, heavily obscured, clumpy starburst systems like SPT0311-58 likely represent the early phases in the formation of massive high-z bulge/spheroids and luminous quasars.

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arXiv2022

Low-power jet-ISM interaction in NGC 7319 revealed by JWST/MIRI MRS

We present JWST/MIRI MRS spectroscopy of NGC7319, the largest galaxy in the Stephan's Quintet, observed as part of the Early Release Observations (ERO). NGC7319 hosts a type 2 active galactic nucleus (AGN) and a low-power radio jet (L_1.4GHz=3.3x10^22 W Hz^-1) with two asymmetric radio hotspots at 430 pc (N2) and 1.5 kpc (S2) projected distances from the unresolved radio core. The MRS data suggest that the molecular material in the disk of the galaxy decelerates the jet and causes this length asymmetry. We find enhanced emission from warm and hot H_2 (T_w=330+-40 K, T_h=900+-60 K) and ionized gas at the intersection between the jet axis and dust lanes in the disk. This emission is coincident with the radio hotspot N2, the hotspot closer to the core, suggesting that the jet-interstellar medium (ISM) interaction decelerates the jet. Conversely, the mid-infrared emission at the more distant hotspot is fainter, more highly ionized, and with lower H_2 excitation, suggesting a more diffuse atomic environment where the jet can progress to farther distances. At the N2 radio hotspot, the ionized gas mass (M_ion=(2.4-12)x10^5 Msun) is comparable to that of the warm H_2, but the former is more turbulent (sigma_ion~300 vs. sigma_H2~150 km/s), so the mechanical energy of the ionized gas is ~1.3-10 times higher. From these estimates, we find that only <1% of the jet energy remains as mechanical energy in these two ISM phases at N2. We also find extended (r>0.3-1.5 kpc) high-ionization emission ([MgV], [NeVI], and [NeV]) close to the radio hotspots. This initial analysis of NGC7319 shows the potential of MIRI/MRS to investigate the AGN feedback mechanisms due to radio jets and their radiation field in the, often heavily dust-enshrouded, central regions of galaxies. Understanding these mechanisms is an essential ingredient in the development of cosmological simulations of galaxy evolution.

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arXiv2021

Detection of an ionized gas outflow in the extreme UV-luminous star-forming galaxy BOSS-EUVLG1 at z=2.47

BOSS-EUVLG1 is the most ultraviolet (UV) and Ly$α$ luminous galaxy detected so far in the Universe, going through a very active starburst phase, and forming stars at a rate (SFR) of 955 $\pm$ 118 M$_{\odot}$ yr$^{-1}$. We report the detection of a broad H$α$ component carrying 25% of the total H$α$ flux. The broad H$α$ line traces a fast and massive ionized gas outflow characterized by a total mass, $\log(M_{out}[M_{\odot}]),$ of 7.94 $\pm$ 0.15, an outflowing velocity (V$_{out}$) of 573 $\pm$ 151 km s$^{-1}$, and an outflowing mass rate ($\dot{M}_{out}$) of 44 $\pm$ 20 M$_{\odot}$ yr$^{-1}$. The presence of the outflow in BOSS-EUVLG1 is also supported by the identification of blueshifted UV absorption lines in low and high ionization states. The energy involved in the H$α$ outflow can be explained by the ongoing star formation without the need for an Active Galactic Nucleus. The derived low mass loading factor ($η$= 0.05 $\pm$ 0.03) indicates that although massive, this phase of the outflow can not be relevant for the quenching of the star formation. In addition, only a small fraction ($\leq$ 15%) of the ionized outflowing material with velocities above 372 km s$^{-1}$ could escape the gravitational potential, and enrich the surrounding circum-galactic medium at distances above tens of kpc. The ionized phase of the outflow does not carry the mass and energy to play a relevant role neither in the evolution of the host galaxy nor in the enrichment of the intergalactic medium. Other phases of the outflow could be carrying most of the outflow energy and mass in the form of hot X-ray emitting gas as predicted by some recent simulations. The expected emission of the extended X-ray emitting halo associated with the outflow in BOSS-EUVLG1 and similar galaxies could be detected with the future X-ray observatory, {\it ATHENA} but could not be resolved spatially.

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arXiv2019

Rest-frame UV Properties of Luminous Strong Gravitationally Lensed Ly$α$ Emitters from the BELLS GALLERY Survey

We present deep rest-frame UV spectroscopic observations using the Gran Telescopio Canarias of six gravitationally lensed Lya emitters (LAEs) at $2.36<z<2.82$ selected from the BELLS GALLERY survey. By taking the magnifications into account, we show that LAEs can be as luminous as L(Lya) = 30x10$^{42}$ erg s-1 and M(UV) = -23 (AB) without invoking an AGN component, in contrast with previous findings. We measure Lya rest-frame equivalent widths, EW(Lya), ranging from 16Åto 50Åand Lya escape fractions, fesc(Lya), from 10% to 40%. Large EW(Lya) and fesc(Lya) are found predominantly in LAEs showing weak low-ionization ISM absorption (EW < 1Å) and narrow Lya profiles (< 300 km s-1 FWHM) with their peak close (< 80 km s-1) to their systemic redshifts, suggestive of less scatter from low HI column densities that favours the escape of Lya photons. We infer stellar metallicities of Z/Zsun ~ 0.2 in almost all LAEs by comparing the P-Cygni profiles of the wind lines NV1240Åand CIV1549Åwith those from stellar synthesis models. We also find a trend between M(UV) and the velocity offset of ISM absorption lines, such as the most luminous LAEs experience stronger outflows. The most luminous LAEs show star formation rates up to 180 Msun yr-1, yet they appear relatively blue ($β$(UV) ~ -1.8 to -2.0) showing evidence of little dust attenuation (E(B-V) = 0.10-0.14). These luminous LAEs may be particular cases of young starburst galaxies that have had no time to form large amounts of dust. If so, they are ideal laboratories to study the early phase of massive star formation, stellar and dust mass growth, and chemical enrichment histories of starburst galaxies at high-z.

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arXiv2019

Investigating the physical properties of galaxies in the Epoch of Reionization with MIRI/JWST spectroscopy

The James Webb Space Telescope will provide deep imaging and spectroscopy for sources at redshifts above 6, covering the Epoch of Reionization (EoR, 6 < z < 10). The Mid-IR instrument (MIRI) integral field spectrograph (MRS) will be the only instrument on board JWST able to observe the brightest optical emission lines H$α$ and [OIII]0.5007$μ$m at redshifts above 7 and 9, respectively. This paper presents a study of the H$α$ fluxes predicted by FIRSTLIGHT cosmological simulations for galaxies at redshifts of 6.5 to 10.5, and its detectability with MIRI. Deep (40 ks) spectroscopic integrations with MRS will be able to detect (S/N > 5) EoR sources at redshifts above 7 with intrinsic star formation rates of more than 2 M$_{\odot}$ yr$^{-1}$, and stellar masses above 4-9 $\times$ 10$^7$ M$_{\odot}$. In addition, the paper presents realistic MRS simulated observations of the expected (rest-frame) optical and near-infrared spectra for some spectroscopically confirmed EoR sources detected by ALMA as [OIII]88$μ$m emitters. The MRS simulated spectra cover a wide range of low metallicities from about 0.2 to 0.02Z$_{\odot}$, and different [OIII]88$μ$m/[OIII]0.5007$μ$m line ratios. The simulated 10ks MRS spectra show S/N in the range of 5 to 90 for H$β$, [OIII]0.4959,0.5007$μ$m, H$α$ and HeI1.083$μ$m emission lines of MACS1149-JD1 at z = 9.11, independent of metallicity. In addition, deep 40 ks simulated spectra of the luminous merger candidate B14-65666 at z=7.15 shows the MRS capabilities of detecting, or putting strong upper limits, on the [NII]0.6584$μ$m, [SII]0.6717,0.6731$μ$m, and [SIII]0.9069,0.9532$μ$m emission lines. In summary, MRS will enable the detailed study of key physical properties like internal extinction, instantaneous star formation, hardness of the ionising continuum, and metallicity, in bright (intrinsic or lensed) EoR sources.

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arXiv2018

Towards a census of high-redshift dusty galaxies with $\mathit{Herschel}$: A selection of "500 $μ$m-risers"

$\mathit{Herschel}$ extragalactic surveys offer a unique opportunity to efficiently select a significant number of rare and massive dusty objects, and thus gain insight into the prodigious star-forming activity that takes place in the very distant Universe. To search for $z\geq4$ dusty star-forming galaxies, in this work we consider red SPIRE objects with fluxes rising from 250 $μ$m to $500\:μ$m (so-called "500 $μ$m-risers"). We aim to implement a novel method to obtain a statistical sample of "500 $μ$m-risers" and fully evaluate our selection inspecting different models of galaxy evolution. We consider one of the largest and deepest ${\it Herschel}$ surveys, the Herschel Virgo Cluster Survey. We develop a novel selection algorithm which links the source extraction and spectral energy distribution fitting. We select 133 "500 $μ$m-risers" over 55 deg$^{2}$, imposing the criteria: $S_{500}>S_{350}>S_{250}$, $S_{250}>13.2$ mJy and $S_{500}>$30 mJy. Differential number counts are in a fairly good agreement with models, displaying better match than other existing samples. In order to interpret the statistical properties of selected sources, which has been proven as a very challenging task due the complexity of observed artefacts, we make end-to-end simulations including physical clustering and lensing. The estimated fraction of strongly lensed sources is $24^{+6}_{-5}\%$ based on models. We present the faintest known statistical sample of "500 $μ$m-risers" and show that noise and strong lensing have crucial impact on measured counts and redshift distribution of selected sources. We estimate the flux-corrected star formation rate density at $4 4$ sources.

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arXiv2017

Characterizing the UV-to-NIR shape of the dust attenuation curve of IR luminous galaxies up to z$\sim$2

In this work we investigate the far-UV to NIR shape of the dust attenuation curve of a sample of IR selected dust obscured (U)LIRGs at z$\sim$2. The spectral energy distributions (SEDs) are fitted with CIGALE, a physically-motivated spectral synthesis model based on energy balance. Its flexibility allows us to test a wide range of different analytical prescriptions for the dust attenuation curve, including the well-known Calzetti and Charlot & Fall curves, and modified versions of them. The attenuation curves computed under the assumption of our reference double power-law model are in very good agreement with those derived, in previous works, with radiative transfer (RT) SED fitting. We investigate the position of our galaxies in the IRX-$β$ diagram and find this to be consistent with grayer slopes, on average, in the UV. We also find evidence for a flattening of the attenuation curve in the NIR with respect to more classical Calzetti-like recipes. This larger NIR attenuation yields larger derived stellar masses from SED fitting, by a median factor of $\sim$ 1.4 and up to a factor $\sim$10 for the most extreme cases. The star formation rate appears instead to be more dependent on the total amount of attenuation in the galaxy. Our analysis highlights the need for a flexible attenuation curve when reproducing the physical properties of a large variety of objects.

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arXiv2017

Multiwavelength characterisation of an ACT-selected, lensed dusty star-forming galaxy at z=2.64

We present \ci\,(2--1) and multi-transition $^{12}$CO observations of a dusty star-forming galaxy, ACT\,J2029+0120, which we spectroscopically confirm to lie at $z$\,=\,2.64. We detect CO(3--2), CO(5--4), CO(7--6), CO(8--7), and \ci\,(2--1) at high significance, tentatively detect HCO$^{+}$(4--3), and place strong upper limits on the integrated strength of dense gas tracers (HCN(4--3) and CS(7--6)). Multi-transition CO observations and dense gas tracers can provide valuable constraints on the molecular gas content and excitation conditions in high-redshift galaxies. We therefore use this unique data set to construct a CO spectral line energy distribution (SLED) of the source, which is most consistent with that of a ULIRG/Seyfert or QSO host object in the taxonomy of the \textit{Herschel} Comprehensive ULIRG Emission Survey. We employ RADEX models to fit the peak of the CO SLED, inferring a temperature of T$\sim$117 K and $n_{\text{H}_2}\sim10^5$ cm$^{-3}$, most consistent with a ULIRG/QSO object and the presence of high density tracers. We also find that the velocity width of the \ci\ line is potentially larger than seen in all CO transitions for this object, and that the $L'_{\rm C\,I(2-1)}/L'_{\rm CO(3-2)}$ ratio is also larger than seen in other lensed and unlensed submillimeter galaxies and QSO hosts; if confirmed, this anomaly could be an effect of differential lensing of a shocked molecular outflow.

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arXiv2015

Dust properties of Lyman break galaxies at $z\sim3$

We explore from a statistical point of view the far-infrared (far-IR) and sub-millimeter (sub-mm) properties of a large sample of LBGs (22,000) at z~3 in the COSMOS field. The large number of galaxies allows us to split it in several bins as a function of UV luminosity, UV slope, and stellar mass to better sample their variety. We perform stacking analysis in PACS (100 and 160 um), SPIRE (250, 350 and 500 um) and AzTEC (1.1 mm) images. Our stacking procedure corrects the biases induced by galaxy clustering and incompleteness of our input catalogue in dense regions. We obtain the full IR spectral energy distributions (SED) of subsamples of LBGs and derive the mean IR luminosity as a function of UV luminosity, UV slope, and stellar mass. The average IRX is roughly constant over the UV luminosity range, with a mean of 7.9 (1.8 mag). However, it is correlated with UV slope, and stellar mass. We investigate using a statistically-controlled stacking analysis as a function of (stellar mass, UV slope) the dispersion of the IRX-UVslope and IRX-M* plane. Our results enable us to study the average relation between star-formation rate (SFR) and stellar mass, and we show that our LBG sample lies on the main sequence of star formation at z~3.

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arXiv2015

HerMES: Current Cosmic Infrared Background Estimates Can be Explained by Known Galaxies and their Faint Companions at z < 4

We report contributions to cosmic infrared background (CIB) intensities originating from known galaxies and their faint companions at submillimeter wavelengths. Using the publicly-available UltraVISTA catalog, and maps at 250, 350, and 500 μm from the \emph{Herschel} Multi-tiered Extragalactic Survey (HerMES), we perform a novel measurement that exploits the fact that uncatalogued sources may bias stacked flux densities --- particularly if the resolution of the image is poor --- and intentionally smooth the images before stacking and summing intensities. By smoothing the maps we are capturing the contribution of faint (undetected in K_S ~ 23.4) sources that are physically associated, or correlated, with the detected sources. We find that the cumulative CIB increases with increased smoothing, reaching 9.82 +- 0.78, 5.77 +- 0.43, and 2.32 +- 0.19$\, \rm nW m^{-2} sr^{-1}$ at 250, 350, and 500 μm at 300 arcsec FWHM. This corresponds to a fraction of the fiducial CIB of 0.94 +- 0.23, 1.07 +- 0.31, and 0.97 +- 0.26 at 250, 350, and 500 μm, where the uncertainties are dominated by those of the absolute CIB. We then propose, with a simple model combining parametric descriptions for stacked flux densities and stellar mass functions, that emission from galaxies with log(M/Msun) > 8.5 can account for the most of the measured total intensities, and argue against contributions from extended, diffuse emission. Finally, we discuss prospects for future survey instruments to improve the estimates of the absolute CIB levels, and observe any potentially remaining emission at z > 4.

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