arXiv subjects

Eva Schinnerer

Publications and source records attributed to Eva Schinnerer.

At least 199 records · Page 11Linked to original sources

arXiv2019

Calibrating star-formation rate prescriptions at different scales (10 pc to 1 kpc) in M31

We calibrate commonly used star formation rate (SFR) prescriptions using observations in five kpc-sized fields in the nearby galaxy Andromeda (M31) at 10\,pc spatial resolution. Our observations at different scales enable us to resolve the star-forming regions and to distinguish them from non star-forming components. We use extinction corrected H$α$ from optical integral field spectroscopy as our reference tracer and have verified its reliability via tests. It is used to calibrate monochromatic and hybrid (H$α$+a$\times$IR and FUV+b$\times$IR) SFR prescriptions, which use FUV (GALEX), 22\,$μ$m (WISE) and 24\,$μ$m (MIPS). Additionally, we evaluate other multi-wavelength infra-red tracers. Our results indicate that the SFR prescriptions do not change (in M31) with spatial scales or with subtraction of the diffuse component. For the calibration factors in the hybrid SFR prescriptions, we find a$\approx$0.2 and b$\approx$22 in M31, which are a factor of 5 higher than in the literature. As the fields in M31 exhibit high attenuation and low dust temperatures, lie at large galacto-centric distances, and suffer from high galactic inclination compared to measurements in other galaxies, we propose that the fields probe a dust layer extended along the line of sight that is not directly spatially associated with star-forming regions. This (vertically) extended dust component increases the attenuation and alters the SFR prescriptions in M31 compared to literature measurements. We recommend that SFR prescriptions should be applied with caution at large galacto-centric distances and in highly inclined galaxies, due to variations in the relative (vertical) distribution of dust and gas.

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arXiv2018

Two Orders of Magnitude Variation in the Star Formation Efficiency Across the Pre-Merger Galaxy NGC 2276

We present the first spatially resolved (~0.5 kpc) measurements of the molecular gas depletion time $τ_{depl}$ across the disk of the interacting spiral galaxy NGC\,2276, a system with an asymmetric morphology in various SFR tracers. To estimate $τ_{depl}$, we use new NOEMA observations of the $^{12}$CO(1-0) emission tracing the bulk molecular gas reservoir in NGC 2276, and extinction-corrected H$α$ measurements obtained with the PMAS/PPaK integral field unit for robust estimates of the SFR. We find a systematic decrease in $τ_{depl}$ of 1-1.5 dex across the disk of NGC 2276, with a further, abrupt drop in $τ_{depl}$ of ~1 dex along the galaxy's western edge. The global $τ_{depl}$ in NGC 2776 is $τ_{depl}=0.55$ Gyr, insistent with literature measurements for the nearby galaxy population. Such a large range in $τ_{depl}$ on sub-kpc scales has never previously been observed within an individual isolated or pre-merger system. When using a metallicity-dependent molecular gas conversion factor X$\rm_{CO}$ the variation decreases by 0.5 dex. We attribute the variation in $τ_{depl}$ to the influence of galactic-scale tidal forces and ram pressure on NGC 2276's molecular interstellar medium (ISM). Our observations add to the growing body of numerical and observational evidence that galaxy-galaxy interactions significantly modify the molecular gas properties and star-forming activity within galactic disks throughout the interaction, and not just during the final merger phase.

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arXiv2018

Diagnostics of a Nuclear Starburst: Water and Methanol Masers

We test models of starburst driven outflows using observations of the 22.2 GHz H$_2$O and 36.2 GHz class I CH$_3$OH maser lines. We have observed the starburst galaxy NGC 253 using the Karl G. Jansky Very Large Array. We present evidence for entrainment of star-forming dense-molecular gas in the outflow of NGC 253. We also show that H$_2$O masers are associated with forming super star clusters and not with supernova remnants. We detect four new 36 GHz CH$_3$OH masers in the central kpc and show possible evidence for a star-formation origin of two class I CH$_3$OH masers. Such high resolution observations are essential for understanding the origin of these masers.

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arXiv2018

Do Spectroscopic Dense Gas Fractions Track Molecular Cloud Surface Densities?

We use ALMA and IRAM 30-m telescope data to investigate the relationship between the spectroscopically-traced dense gas fraction and the cloud-scale (120 pc) molecular gas surface density in five nearby, star-forming galaxies. We estimate the dense gas mass fraction at 650 pc and 2800 pc scales using the ratio of HCN (1-0) to CO (1-0) emission. We then use high resolution (120 pc) CO (2-1) maps to calculate the mass-weighted average molecular gas surface density within 650 pc or 2770 pc beam where the dense gas fraction is estimated. On average, the dense gas fraction correlates with the mass-weighted average molecular gas surface density. Thus, parts of a galaxy with higher mean cloud-scale gas surface density also appear to have a larger fraction of dense gas. The normalization and slope of the correlation do vary from galaxy to galaxy and with the size of the regions studied. This correlation is consistent with a scenario where the large-scale environment sets the gas volume density distribution, and this distribution manifests in both the cloud-scale surface density and the dense gas mass fraction.

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arXiv2018

The VLA-COSMOS 3 GHz Large Project: Star formation properties and radio luminosity functions of AGN with moderate-to-high radiative luminosities out to $z\sim6$

We study a sample of 1,604 moderate-to-high radiative luminosity active galactic nuclei (HLAGN) selected at 3 GHz within the VLA-COSMOS 3 GHz Large Project. These were classified by combining multiple AGN diagnostics: X-ray data, mid-infrared data and broad-band spectral energy distribution fitting. We decompose the total radio 1.4 GHz luminosity ($\mathrm{L_{1.4\ GHz,TOT}}$) into the emission originating from star formation and AGN activity by measuring the excess in $\mathrm{L_{1.4\ GHz,TOT}}$ relative to the infrared-radio correlation of star-forming galaxies. To quantify the excess, for each source we calculate the AGN fraction ($\mathrm{f_{AGN}}$), the fractional contribution of AGN activity to $\mathrm{L_{1.4\ GHz,TOT}}$. The majority of the HLAGN, $(68.0\pm1.5)\%$, are dominated by star-forming processes ($f_{AGN}\leq0.5$), while $(32.0\pm1.5)\%$ are dominated by AGN-related radio emission ($0.5 0$).

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arXiv2018

Science with an ngVLA: Molecular Clouds in Galaxies

Stars form in cold clouds of predominantly molecular (H2) gas. We are just beginning to understand how the formation, properties, and destruction of these clouds varies across the universe. In this chapter, we describe how the thermal line imaging capabilities of the proposed next generation Very Large Array (ngVLA) could make major contributions to this field. Looking at CO emission, the proposed ngVLA would be able to quickly survey the bulk properties of molecular clouds across the whole nearby galaxy population. This includes many unique very nearby northern targets (e.g., Andromeda) inaccessible to ALMA. Such surveys offer a main observational constraint on the formation, destruction, lifetime, and star formation properties of clouds. Targeting specific regions, the ngVLA will also be able to heavily resolve clouds in the nearest galaxies. This will allow detailed studies of the substructure and kinematics --- and so the internal physics --- of clouds across different chemical and dynamical environments.

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arXiv2018

Science with an ngVLA: Radio Continuum Emission from Galaxies: An Accounting of Energetic Processes

Radio continuum observations have proven to be a workhorse in our understanding of the star formation process (i.e., stellar birth and death) from galaxies both in the nearby universe and out to the highest redshifts. In this article we focus on how the ngVLA will transform our understanding of star formation by enabling one to map and decompose the radio continuum emission from large, heterogeneous samples of nearby galaxies on $\gtrsim 10$\,pc scales to conduct a proper accounting of the energetic processes powering it. At the discussed sensitivity and angular resolution, the ngVLA will simultaneously be able to create maps of current star formation activity at $\sim$100\,pc scales, as well as detect and characterize (e.g., size, spectral shape, density, etc.) discrete H{\sc ii} regions and supernova remnants on 10\,pc scales in galaxies out to the distance of the Virgo cluster. Their properties can then be used to see how they relate to the local and global ISM and star formation conditions. Such investigations are essential for understanding the astrophysics of high-$z$ measurements of galaxies, allowing for proper modeling of galaxy formation and evolution.

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arXiv2018

"Super-deblended" Dust Emission in Galaxies: II. Far-IR to (sub)millimeter photometry and high redshift galaxy candidates in the full COSMOS field

We present a "super-deblended" far-infrared to (sub)millimeter photometric catalog in the Cosmic Evolution Survey (COSMOS), prepared with the method recently developed by Liu et al. 2018, with key adaptations. We obtain point spread function (PSF) fitting photometry at fixed prior positions including 88,008 galaxies detected in either VLA 1.4~GHz, 3~GHz and/or MIPS 24~$μ$m images. By adding a specifically carved mass-selected sample (with an evolving stellar mass limit), a highly complete prior sample of 194,428 galaxies is achieved for deblending FIR/(sub)mm images. We performed ``active' removal of non relevant priors at FIR/(sub)mm bands using spectral energy distribution (SED) fitting and redshift information. In order to cope with the shallower COSMOS data we subtract from the maps the flux of faint non-fitted priors and explicitly account for the uncertainty of this step. The resulting photometry (including data from Spitzer, Herschel, SCUBA2, AzTEC, MAMBO and NSF's Karl G. Jansky Very Large Array at 3~GHz and 1.4~GHz) displays well behaved quasi-Gaussian uncertainties, calibrated from Monte Carlo simulations and tailored to observables (crowding, residual maps). Comparison to ALMA photometry for hundreds of sources provide a remarkable validation of the technique. We detect 11,220 galaxies over the 100--1200~$μ$m range, extending to $z_{\rm phot}\sim7$. We conservatively selected a sample of 85 $z>4$ high redshift candidates, significantly detected in the FIR/(sub)mm, often with secure radio and/or Spitzer/IRAC counterparts. This provides a chance to investigate the first generation of vigorous starburst galaxies (SFRs$\sim1000\mathrm{M}_\odot$~yr$^{-1}$). The photometric and value added catalogs are publicly released.

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arXiv2018

Azimuthal variations of gas-phase oxygen abundance in NGC 2997

The azimuthal variation of the HII region oxygen abundance in spiral galaxies is a key observable for understanding how quickly oxygen produced by massive stars can be dispersed within the surrounding interstellar medium. Observational constraints on the prevalence and magnitude of such azimuthal variations remain rare in the literature. Here, we report the discovery of pronounced azimuthal variations of HII region oxygen abundance in NGC 2997, a spiral galaxy at approximately 11.3 Mpc. Using 3D spectroscopic data from the TYPHOON Program, we study the HII region oxygen abundance at a physical resolution of 125 pc. Individual HII regions or complexes are identified in the 3D optical data and their strong emission line fluxes measured to constrain their oxygen abundances. We find 0.06 dex azimuthal variations in the oxygen abundance on top of a radial abundance gradient that is comparable to those seen in other star-forming disks. At a given radial distance, the oxygen abundances are highest in the spiral arms and lower in the inter-arm regions, similar to what has been reported in NGC 1365 using similar observations. We discuss whether the azimuthal variations could be recovered when the galaxy is observed at worse physical resolutions and lower signal-to-noise ratios.

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arXiv2018

The Star Formation Efficiency per Free Fall Time in Nearby Galaxies

We estimate the star formation efficiency per gravitational free fall time, $ε_{\rm ff}$, from observations of nearby galaxies with resolution matched to the typical size of a Giant Molecular Cloud. This quantity, $ε_{\rm ff}$, is theoretically important but so far has only been measured for Milky Way clouds or inferred indirectly in a few other galaxies. Using new, high resolution CO imaging from the PHANGS-ALMA survey, we estimate the gravitational free-fall time at 60 to 120 pc resolution, and contrast this with the local molecular gas depletion time to estimate $ε_{\rm ff}$. Assuming a constant thickness of the molecular gas layer ($H = 100$ pc) across the whole sample, the median value of $ε_{\rm ff}$ in our sample is $0.7\%$. We find a mild scale-dependence, with higher $ε_{\rm ff}$ measured at coarser resolution. Individual galaxies show different values of $ε_{\rm ff}$, with the median $ε_{\rm ff}$ ranging from $0.3\%$ to $2.6\%$. We find the highest $ε_{\rm ff}$ in our lowest mass targets, reflecting both long free-fall times and short depletion times, though we caution that both measurements are subject to biases in low mass galaxies. We estimate the key systematic uncertainties, and show the dominant uncertainty to be the estimated line-of-sight depth through the molecular gas layer and the choice of star formation tracers.

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arXiv2018

Hidden in plain sight: a massive, dusty starburst in a galaxy protocluster at z=5.7 in the COSMOS field

We report the serendipitous discovery of a dusty, starbursting galaxy at $z=5.667$ (hereafter called CRLE) in close physical association with the "normal" main-sequence galaxy HZ10 at $z=5.654$. CRLE was identified by detection of [CII], [NII] and CO(2-1) line emission, making it the highest redshift, most luminous starburst in the COSMOS field. This massive, dusty galaxy appears to be forming stars at a rate of at least 1500$\,M_\odot$ yr$^{-1}$ in a compact region only $\sim3$ kpc in diameter. The dynamical and dust emission properties of CRLE suggest an ongoing merger driving the starburst, in a potentially intermediate stage relative to other known dusty galaxies at the same epoch. The ratio of [CII] to [NII] may suggest that an important ($\sim15\%$) contribution to the [CII] emission comes from a diffuse ionized gas component, which could be more extended than the dense, starbursting gas. CRLE appears to be located in a significant galaxy overdensity at the same redshift, potentially associated with a large-scale cosmic structure recently identified in a Lyman Alpha Emitter survey. This overdensity suggests that CRLE and HZ10 reside in a protocluster environment, offering the tantalizing opportunity to study the effect of a massive starburst on protocluster star formation. Our findings support the interpretation that a significant fraction of the earliest galaxy formation may occur from the inside out, within the central regions of the most massive halos, while rapidly evolving into the massive galaxy clusters observed in the local Universe.

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arXiv2018

Cloud-Scale Molecular Gas Properties in 15 Nearby Galaxies

We measure the velocity dispersion, $σ$, and surface density, $Σ$, of the molecular gas in nearby galaxies from CO spectral line cubes with spatial resolution $45$-$120$ pc, matched to the size of individual giant molecular clouds. Combining $11$ galaxies from the PHANGS-ALMA survey with $4$ targets from the literature, we characterize ${\sim}30,000$ independent sightlines where CO is detected at good significance. $Σ$ and $σ$ show a strong positive correlation, with the best-fit power law slope close to the expected value for resolved, self-gravitating clouds. This indicates only weak variation in the virial parameter $α_\mathrm{vir}\proptoσ^2/Σ$, which is ${\sim}1.5$-$3.0$ for most galaxies. We do, however, observe enormous variation in the internal turbulent pressure $P_\mathrm{turb}\proptoΣ\,σ^2$, which spans ${\sim}5\rm\;dex$ across our sample. We find $Σ$, $σ$, and $P_\mathrm{turb}$ to be systematically larger in more massive galaxies. The same quantities appear enhanced in the central kpc of strongly barred galaxies relative to their disks. Based on sensitive maps of M31 and M33, the slope of the $σ$-$Σ$ relation flattens at $Σ\lesssim10\rm\;M_\odot\,pc^{-2}$, leading to high $σ$ for a given $Σ$ and high apparent $α_\mathrm{vir}$. This echoes results found in the Milky Way, and likely originates from a combination of lower beam filling factors and a stronger influence of local environment on the dynamical state of molecular gas in the low density regime.

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arXiv2018

Survey of Water and Ammonia in Nearby galaxies (SWAN): Resolved Ammonia Thermometry, and Water and Methanol Masers in IC 342, NGC 6946 and NGC 2146

The Survey of Water and Ammonia in Nearby galaxies (SWAN) studies atomic and molecular species across the nuclei of four star forming galaxies: NGC\,253, IC\,342, NGC\,6946, and NGC\,2146. As part of this survey, we present Karl G. Jansky Very Large Array (VLA) molecular line observations of three galaxies: IC\,342, NGC\,6946 and NGC\,2146. NGC\,253 is covered in a previous paper. These galaxies were chosen to span an order of magnitude in star formation rates and to select a variety of galaxy types. We target the metastable transitions of ammonia NH$_{3}$(1,1) to (5,5), the 22\,GHz water (H$_2$O) ($6_{16}-5_{23}$) transition, and the 36.1\,GHz methanol (CH$_3$OH) ($4_{-1}-3_{0}$) transition. {We use the NH$_{3}$\ metastable lines to perform thermometry of the dense molecular gas.} We show evidence for uniform heating across the central kpc of IC\,342 with two temperature components for the molecular gas, similar to NGC 253,} of 27\,K and 308\,K, and that the dense molecular gas in NGC\,2146 has a temperature $<$86 K. We identify two new water masers in IC\,342, and one new water maser in each of NGC\,6946 and NGC\,2146. The two galaxies NGC\,253 and NGC\,2146, with the most vigorous star formation, host H$_2$O kilomasers. Lastly, we detect the first 36\,GHz CH$_3$OH\ masers in IC\,342 and NGC\,6946. For the four external galaxies the total CH$_3$OH\ luminosity in each galaxy suggests a correlation with galactic star formation rate, whereas the morphology of the emission is similar to that of HNCO, a weak shock tracer.

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arXiv2018

Dense Gas, Dynamical Equilibrium Pressure, and Star Formation in Nearby Star-Forming Galaxies

We use new ALMA observations to investigate the connection between dense gas fraction, star formation rate, and local environment across the inner region of four local galaxies showing a wide range of molecular gas depletion times. We map HCN (1-0), HCO$^+$ (1-0), CS (2-1), $^{13}$CO (1-0), and C$^{18}$O (1-0) across the inner few kpc of each target. We combine these data with short spacing information from the IRAM large program EMPIRE, archival CO maps, tracers of stellar structure and recent star formation, and recent HCN surveys by Bigiel et al. and Usero et al. We test the degree to which changes in the dense gas fraction drive changes in the SFR. $I_{HCN}/I_{CO}$ (tracing the dense gas fraction) correlates strongly with $I_{CO}$ (tracing molecular gas surface density), stellar surface density, and dynamical equilibrium pressure, $P_{DE}$. Therefore, $I_{HCN}/I_{CO}$ becomes very low and HCN becomes very faint at large galactocentric radii, where ratios as low as $I_{HCN}/I_{CO} \sim 0.01$ become common. The apparent ability of dense gas to form stars, $Σ_{SFR}/Σ_{dense}$ (where $Σ_{dense}$ is traced by the HCN intensity and the star formation rate is traced by a combination of H$α$ and 24$μ$m emission), also depends on environment. $Σ_{SFR}/Σ_{dense}$ decreases in regions of high gas surface density, high stellar surface density, and high $P_{DE}$. Statistically, these correlations between environment and both $Σ_{SFR}/Σ_{dense}$ and $I_{HCN}/I_{CO}$ are stronger than that between apparent dense gas fraction ($I_{HCN}/I_{CO}$) and the apparent molecular gas star formation efficiency $Σ_{SFR}/Σ_{mol}$. We show that these results are not specific to HCN.

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arXiv2018

Average radio spectral energy distribution of highly star-forming galaxies

The infrared-radio correlation (IRRC) offers a way to assess star formation from radio emission. Multiple studies found the IRRC to decrease with increasing redshift. This may in part be due to the lack of knowledge about the possible radio spectral energy distributions (SEDs) of star-forming galaxies. We constrain the radio SED of a complete sample of highly star-forming galaxies ($SFR>100\,\mathrm{M_{\odot}}/\,\mathrm{yr}$) based on the VLA-COSMOS $1.4\,\mathrm{GHz}$ Joint and $3\,\mathrm{GHz}$ Large Project catalogs. We reduce archival GMRT $325\,\mathrm{MHz}$ and $610\,\mathrm{MHz}$ observations, broadening the rest-frame frequency range to $0.3-15\,\mathrm{GHz}$. Employing survival analysis and fitting a double power law SED, we find that the slope steepens from a spectral index of $α_1=0.51\pm 0.04$ below $4.5\,\mathrm{GHz}$ to $α_2=0.98\pm0.07$ above $4.5\,\mathrm{GHz}.$ Our results suggest that the use of a K-correction assuming a single power-law radio SED for star forming galaxies is likely not the root cause of the IRRC trend.

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arXiv2017

A Model for the Onset of Self-gravitation and Star Formation in Molecular Gas Governed by Galactic Forces: I. Cloud-scale Gas Motions

Modern extragalactic molecular gas surveys now reach the scales of star-forming giant molecular clouds (GMCs, 20-50 pc). Systematic variations in GMC properties with galaxy environment imply that clouds are not universally self-gravitating objects, decoupled from their surroundings. Here we reexamine the coupling of clouds to their environment and develop a model for 3D gas motions generated by forces arising with the galaxy gravitational potential defined by the background disk of stars and dark matter. We show that these motions can resemble or even exceed the motions needed to support gas against its own self-gravity throughout typical galaxy disks. The importance of the galactic potential in spiral arms and galaxy centers suggests that the response to self-gravity does not always dominate the motions of gas at GMC scales, with implications for observed gas kinematics, virial equilibrium and cloud morphology. We describe how a uniform treatment of gas motions in the plane and in the vertical direction synthesizes the two main mechanisms proposed to regulate star formation: vertical pressure equilibrium and shear/Coriolis forces as parameterized by Toomre Q~1. As the modeled motions are coherent and continually driven by the external potential, they represent support for the gas that is distinct from that conventionally attributed to turbulence, which decays rapidly and requires thus maintenance, e.g. via feedback from star formation. Thus our model suggests the galaxy itself can impose an important limit to star formation, as we explore in a second paper in this series.

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arXiv2017

SDSS-V: Pioneering Panoptic Spectroscopy

SDSS-V will be an all-sky, multi-epoch spectroscopic survey of over six million objects. It is designed to decode the history of the Milky Way, trace the emergence of the chemical elements, reveal the inner workings of stars, and investigate the origin of planets. It will also create an integral-field spectroscopic map of the gas in the Galaxy and the Local Group that is 1,000x larger than the current state of the art and at high enough spatial resolution to reveal the self-regulation mechanisms of galactic ecosystems. SDSS-V will pioneer systematic, spectroscopic monitoring across the whole sky, revealing changes on timescales from 20 minutes to 20 years. The survey will thus track the flickers, flares, and radical transformations of the most luminous persistent objects in the universe: massive black holes growing at the centers of galaxies. The scope and flexibility of SDSS-V will be unique among extant and future spectroscopic surveys: it is all-sky, with matched survey infrastructures in both hemispheres; it provides near-IR and optical multi-object fiber spectroscopy that is rapidly reconfigurable to serve high target densities, targets of opportunity, and time-domain monitoring; and it provides optical, ultra-wide-field integral field spectroscopy. SDSS-V, with its programs anticipated to start in 2020, will be well-timed to multiply the scientific output from major space missions (e.g., TESS, Gaia, eROSITA) and ground-based projects. SDSS-V builds on the 25-year heritage of SDSS's advances in data analysis, collaboration infrastructure, and product deliverables. The project is now refining its science scope, optimizing the survey strategies, and developing new hardware that builds on the SDSS-IV infrastructure. We present here an overview of the current state of these developments as we seek to build our worldwide consortium of institutional and individual members.

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arXiv2017

The infrared-radio correlation of spheroid- and disc-dominated star-forming galaxies to z $\sim$ 1.5 in the COSMOS field

Using infrared data from the Herschel Space Observatory and Karl G. Jansky Very Large Array (VLA) 3 GHz observations in the COSMOS field, we investigate the redshift evolution of the infrared-radio correlation (IRRC) for star-forming galaxies (SFGs) we classify as either spheroid- or disc-dominated based on their morphology. The sample predominantly consists of disc galaxies with stellar mass ${\gtrsim}10^{10}\,M_{\odot}$, and residing on the star-forming main sequence (MS). After the removal of AGN using standard approaches, we observe a significant difference between the redshift-evolution of the median IR/radio ratio $\overline{q}_{\mathrm{TIR}}$ of (i) a sample of ellipticals, plus discs with a substantial bulge component (`spheroid-dominated' SFGs) and, (ii) virtually pure discs and irregular systems (`disc-dominated' SFGs). The spheroid-dominated population follows a declining $\overline{q}_{\mathrm{TIR}}$ vs. $z$ trend similar to that measured in recent evolutionary studies of the IRRC. However, for disc-dominated galaxies, where radio and IR emission should be linked to star formation in the most straightforward way, we measure very little change in $\overline{q}_{\mathrm{TIR}}$. This suggests that low-redshift calibrations of radio emission as an SFR-tracer may remain valid out to at least $z\,{\simeq}\,1\,{-}\,1.5$ for pure star-forming systems. We find that the different redshift-evolution of $q_{\rm TIR}$ for the spheroid- and disc-dominated sample is mainly due to an increasing radio excess for spheroid-dominated galaxies at $z\,{\gtrsim}\,$0.8, hinting at some residual AGN activity in these systems. This finding demonstrates that in the absence of AGN the IRRC is independent of redshift, and that radio observations can therefore be used to estimate SFRs at all redshifts for genuinely star-forming galaxies.

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