Papers by Mark T . Sargent
Looking ahead to the sky with the Square Kilometre Array: simulating flux densities and resolved radio morphologies of 0 < z < 2.5 star-forming galaxies
Monthly Notices of the Royal Astronomical Society
SKA-MID surveys will be the first in the radio domain to achieve clearly sub-arcsecond resolution... more SKA-MID surveys will be the first in the radio domain to achieve clearly sub-arcsecond resolution at high sensitivity over large areas, opening new science applications for galaxy evolution. To investigate the potential of these surveys, we create simulated SKA-MID images of a ∼0.04 deg2 region of GOODS-North, constructed using multi-band HST imaging of 1723 real galaxies containing significant substructure at 0 < z < 2.5. We create images at the proposed depths of the band 2 wide, deep, and ultradeep reference surveys (RMS = 1.0, 0.2, and 0.05 μJy over 1000, 10–30, and 1 deg2, respectively), using the telescope response of SKA-MID at 0.6 arcsec resolution. We quantify the star formation rate – stellar mass space the surveys will probe, and asses to which stellar masses the surveys will be complete. We measure galaxy flux density, half-light radius (R50), concentration, Gini (distribution of flux), second-order moment of the brightest pixels (M20), and asymmetry before and aft...
arXiv: Astrophysics of Galaxies, 2018
Deep continuum surveys at radio wavelengths are able to cover large areas, yield high angular res... more Deep continuum surveys at radio wavelengths are able to cover large areas, yield high angular resolution, and do not suffer from dust extinction, thus providing a robust way to measure the star formation history of the universe. However, with the current sensitivities of existing radio telescopes, it remains challenging to detect galaxies that dominate the cosmic star formation history even with extremely long integrations. With the ngVLA, a new portion of parameter space will be opened up for radio continuum surveys: deep (~200 nJy/bm), large-area (~1 deg^2), sub-arcsecond surveys at high frequencies (~8 GHz), where the observed radio emission from high-z galaxies should be dominated by free-free emission, providing a robust measurement for the star formation history of the universe. By being able to image the star formation activity, unbiased by dust, for a large, homogeneous sample of galaxies with a wide range of luminosities into the epoch of reionization, such surveys with the...
The VLA-COSMOS Perspective Of The Radio-IR Relation At z< 1.5
ABSTRACT
The VLA-COSMOS survey. IV. (Schinnerer+, 2010)
The central seven pointings of the mosaic for the VLA-COSMOS Large project (pointing numbers: F07... more The central seven pointings of the mosaic for the VLA-COSMOS Large project (pointing numbers: F07, F08, F11, F12, F13, F16, F17) were observed using the VLA A configuration in 2006 February and March. The observations were executed on 11 days. ------------------------------------ Pointing RA (J2000) DE (J2000) ------------------------------------ F07 10 00 58.62 +02 25 20.42 F08 09 59 58.58 +02 25 20.42 F11 10 01 28.64 +02 12 21.00 F12 10 00 28.60 +02 12 21.00 F13 09 59 28.56 +02 12 21.00 F16 10 00 58.62 +01 59 21.58 F17 09 59 58.58 +01 59 21.58 ------------------------------------ (1 data file).
The Role of Environment in the Growth of Disk Galaxies
ABSTRACT
The Astrophysical Journal Supplement Series, 2010
In the context of the VLA-COSMOS Deep project additional VLA A array observations at 1.4 GHz were... more In the context of the VLA-COSMOS Deep project additional VLA A array observations at 1.4 GHz were obtained for the central degree of the COSMOS field and combined with the existing data from the VLA-COSMOS Large project. A newly constructed Deep mosaic with a resolution of 2.5 ′′ was used to search for sources down to 4σ with 1σ ≈ 12 µJy/beam in the central 50 ′ ×50 ′ . This new catalog is combined with the catalog from the Large project (obtained at 1.5 ′′ ×1.4 ′′ resolution) to construct a new Joint catalog. All sources listed in the new Joint catalog have peak flux densities of ≥5σ at 1.5 ′′ and/or 2.5 ′′ resolution to account for the fact that a significant fraction of sources at these low flux levels are expected to be slighty resolved at 1.5 ′′ resolution. All properties listed in the Joint catalog such as peak flux density, integrated flux density and source size are determined in the 2.5 ′′ resolution Deep image. In addition, the Joint catalog contains 43 newly identified multi-component sources.
arXiv (Cornell University), Oct 6, 2022
Our current understanding of the cosmic star formation history at z > 3 is primarily based on UV-... more Our current understanding of the cosmic star formation history at z > 3 is primarily based on UV-selected galaxies (Lyman-break galaxies, i.e., LBGs). Recent studies of H-dropouts (HST-dark galaxies) have revealed that we may be missing a large proportion of star formation that is taking place in massive galaxies at z > 3. In this work, we extend the H-dropout criterion to lower masses to select optically dark or faint galaxies (OFGs) at high redshifts in order to complete the census between LBGs and H-dropouts. Our criterion (H > 26.5 mag & [4.5] < 25 mag) combined with a de-blending technique is designed to select not only extremely dust-obscured massive galaxies but also normal star-forming galaxies (typically E(B-V) > 0.4) with lower stellar masses at high redshifts. In addition, with this criterion, our sample is not contaminated by massive passive or old galaxies. In total, we identified 27 OFGs at z phot > 3 (with a median of z med = 4.1) in the GOODS-ALMA field, covering a wide distribution of stellar masses with log(M /M ) = 9.4 -11.1 (with a median of log(M med /M ) = 10.3). We find that up to 75% of the OFGs with log(M /M ) = 9.5 -10.5 were neglected by previous LBGs and H-dropout selection techniques. After performing an optical-to-millimeter stacking analysis of the OFGs, we find that rather than being limited to a rare population of extreme starbursts, these OFGs represent a normal population of dusty star-forming galaxies at z > 3. The OFGs exhibit shorter gas depletion timescales, slightly lower gas fractions, and lower dust temperatures than the scaling relation of typical star-forming galaxies. Additionally, the total star formation rate (SFR tot = SFR IR + SFR UV ) of the stacked OFGs is much higher than the SFR corr UV (SFR UV corrected for dust extinction), with an average SFR tot /SFR corr UV = 8 ± 1, which lies above (∼0.3 dex) the 16-84th percentile range of typical star-forming galaxies at 3 ≤ z ≤ 6. All of the above suggests the presence of hidden dust regions in the OFGs that absorb all UV photons, which cannot be reproduced with dust extinction corrections. The effective radius of the average dust size measured by a circular Gaussian model fit in the uv plane is R e(1.13mm) = 1.01 ± 0.05 kpc. After excluding the five LBGs in the OFG sample, we investigated their contributions to the cosmic star formation rate density (SFRD). We found that the SFRD at z > 3 contributed by massive OFGs (log(M /M ) > 10.3) is at least two orders of magnitude higher than the one contributed by equivalently massive LBGs. Finally, we calculated the combined contribution of OFGs and LBGs to the cosmic SFRD at z = 4 -5 to be 4 × 10 -2 M yr -1 Mpc -3 , which is about 0.15 dex (43%) higher than the SFRD derived from UV-selected samples alone at the same redshift. This value could be even larger, as our calculations were performed in a very conservative way.
arXiv (Cornell University), Oct 15, 2018
Radio continuum observations have proven to be a workhorse in our understanding of the star forma... more 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 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 ∼100 pc 1
The Astrophysical Journal, 2022
Radio free–free emission is considered to be one of the most reliable tracers of star formation i... more Radio free–free emission is considered to be one of the most reliable tracers of star formation in galaxies. However, as it constitutes the faintest part of the radio spectrum—being roughly an order of magnitude less luminous than radio synchrotron emission at the GHz frequencies typically targeted in radio surveys—the usage of free–free emission as a star formation rate tracer has mostly remained limited to the local universe. Here, we perform a multifrequency radio stacking analysis using deep Karl G. Jansky Very Large Array observations at 1.4, 3, 5, 10, and 34 GHz in the COSMOS and GOODS-North fields to probe free–free emission in typical galaxies at the peak of cosmic star formation. We find that z ∼ 0.5–3 star-forming galaxies exhibit radio emission at rest-frame frequencies of ∼65–90 GHz that is ∼1.5–2 times fainter than would be expected from a simple combination of free–free and synchrotron emission, as in the prototypical starburst galaxy M82. We interpret this as a defici...
Monthly Notices of the Royal Astronomical Society, 2021
We study the interstellar medium (ISM) properties as a function of the molecular gas size for 77 ... more We study the interstellar medium (ISM) properties as a function of the molecular gas size for 77 infrared-selected galaxies at z ∼ 1.3, having stellar masses 109.4 ≲ M⋆ ≲ 1012.0 M⊙ and star formation rates 12 ≲ SFRFIR ≲ 1000 M⊙ yr−1. Molecular gas sizes are measured on ALMA images that combine CO(2-1), CO(5-4), and underlying continuum observations, and include CO(4-3), CO(7-6) + [CI](3P2 − 3P1), [CI](3P1 − 3P0) observations for a subset of the sample. The $\gtrsim $46 per cent of our galaxies have a compact molecular gas reservoir, and lie below the optical discs mass–size relation. Compact galaxies on and above the main sequence have higher CO excitation and star formation efficiency than galaxies with extended molecular gas reservoirs, as traced by CO(5-4)/CO(2-1) and CO(2-1)/LIR, SF ratios. Average CO + [CI] spectral line energy distributions indicate higher excitation in compacts relative to extended sources. Using CO(2-1) and dust masses as molecular gas mass tracers, and conv...
Monthly Notices of the Royal Astronomical Society, 2021
The infrared-radio correlation (IRRC) underpins many commonly used radio luminosity–star formatio... more The infrared-radio correlation (IRRC) underpins many commonly used radio luminosity–star formation rate (SFR) calibrations. In preparation for the new generation of radio surveys, we revisit the IRRC of low-z galaxies by (a) drawing on the best currently available infrared (IR) and 1.4 GHz radio photometry, plus ancillary data over the widest possible area, and (b) carefully assessing potential systematics. We compile a catalogue of ∼9500, z < 0.2 galaxies and derive their 1.4 GHz radio (L1.4), total IR, and monochromatic IR luminosities in up to seven bands, allowing us to parametrize the wavelength dependence of monochromatic IRRCs from 22–500 µm. For the first time for low-z samples, we quantify how poorly matched IR and radio survey depths bias measured median IR/radio ratios, $\overline{q}_{\mathrm{TIR}}$, and discuss the level of biasing expected for low-z IRRC studies in ASKAP/MeerKAT fields. For our subset of ∼2000 high-confidence star-forming galaxies, we find a median $...
The Astrophysical Journal, 2020
We provide a coherent, uniform measurement of the evolution of the logarithmic star formation rat... more We provide a coherent, uniform measurement of the evolution of the logarithmic star formation rate (SFR)-stellar mass (M * ) relation, called the main sequence (MS) of star-forming galaxies , for star-forming and all galaxies out to z 5. We measure the MS using mean stacks of 3 GHz radio-continuum images to derive average SFRs for∼ 200,000 mass-selected galaxies at z>0.3 in the COSMOS field. We describe the MS relation by adopting a new model that incorporates a linear relation at low stellar mass (log(M * /M e )<10) and a flattening at high stellar mass that becomes more prominent at low redshift (z<1.5). We find that the SFR density peaks at 1.5<z<2, and at each epoch there is a characteristic stellar mass (M * =1-4×10 10 M e ) that contributes the most to the overall SFR density. This characteristic mass increases with redshift, at least to z∼2.5. We find no significant evidence for variations in the MS relation for galaxies in different environments traced by the galaxy number density at 0.3<z<3, nor for galaxies in X-ray groups at z∼0.75. We confirm that massive bulge-dominated galaxies have lower SFRs than disk-dominated galaxies at a fixed stellar mass at z<1.2. As a consequence, the increase in bulge-dominated galaxies in the local star-forming population leads to a flattening of the MS at high stellar masses. This indicates that "mass quenching" is linked with changes in the morphological composition of galaxies at a fixed stellar mass. Unified Astronomy Thesaurus concepts: Galaxy evolution (594); Galaxy quenching (2040); Galaxy bulges (578); Galaxy environments (2029); Radio continuum emission (1340); Extragalactic radio sources (508)
Proceedings of Advancing Astrophysics with the Square Kilometre Array — PoS(AASKA14), 2015
In this chapter, we highlight a number of science investigations that are enabled by the inclusio... more In this chapter, we highlight a number of science investigations that are enabled by the inclusion of Band 5 (4.6-13.8 GHz) for SKA1-MID science operations, while focusing on the astrophysics of star formation over cosmic time. For studying the detailed astrophysics of star formation at highredshift, surveys at frequencies 10 GHz have the distinct advantage over traditional ∼1.4 GHz surveys as they are able to yield higher angular resolution imaging while probing higher rest frame frequencies of galaxies with increasing redshift, where emission of star-forming galaxies becomes dominated by thermal (free-free) radiation. In doing so, surveys carried out at 10 GHz provide a robust, dust-unbiased measurement of the massive star formation rate by being highly sensitive to the number of ionizing photons that are produced. To access this powerful star formation rate diagnostic requires that Band 5 be available for SKA1-MID. We additionally present a detailed science case for frequency coverage extending up to 30 GHz during full SKA2 operations, as this allows for highly diverse science while additionally providing contiguous frequency coverage between the SKA and ALMA, which will likely be the two most powerful interferometers for the coming decades. To enable this synergy, it is crucial that the dish design of the SKA be flexible enough to include the possibility of being fit with receivers operating up to 30 GHz.
The Astrophysical Journal, 2019
We use the results from the ALMA large program ASPECS, the spectroscopic survey in the Hubble Ult... more We use the results from the ALMA large program ASPECS, the spectroscopic survey in the Hubble Ultra Deep Field (HUDF), to constrain CO luminosity functions of galaxies and the resulting redshift evolution of ρ(H 2 ). The broad frequency range covered enables us to identify CO emission lines of different rotational transitions in the HUDF at z > 1. We find strong evidence that the CO luminosity function evolves with redshift, with the knee of the CO luminosity function decreasing in luminosity by an order of magnitude from ∼2 to the local universe. Based on Schechter fits, we estimate that
Monthly Notices of the Royal Astronomical Society, 2017
Using infrared data from the Herschel Space Observatory and Karl G. Jansky Very Large Array (VLA)... more 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 10 10 M , 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 q 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 q 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 q TIR . This suggests that low-redshift calibrations of radio emission as an SFR-tracer may remain valid out to at least z 1 -1.5 for pure star-forming systems. We find that the different redshift-evolution of q TIR for the spheroid-and discdominated sample is mainly due to an increasing radio excess for spheroid-dominated galaxies at z 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.
The Astrophysical Journal, 2018
Galaxy interactions are often accompanied by an enhanced star formation rate (SFR). Since molecul... more Galaxy interactions are often accompanied by an enhanced star formation rate (SFR). Since molecular gas is essential for star formation, it is vital to establish whether, and by how much, galaxy interactions affect the molecular gas properties. We investigate the effect of interactions on global molecular gas properties by studying a sample of 58 galaxies in pairs and 154 control galaxies. Molecular gas properties are determined from observations with the JCMT, PMO, CSO telescopes, and supplemented with data from the xCOLD GASS and JINGLE surveys at 12 CO(1-0) and 12 CO(2-1). The SFR, gas mass (M H2 ), and gas fraction (f gas ) are all enhanced in galaxies in pairs by ∼ 2.5 times compared to the controls matched in redshift, mass, and effective radius, while the enhancement of star formation efficiency (SFE ≡ SFR/M H2 ) is less than a factor of 2. We also find that the enhancements
Monthly Notices of the Royal Astronomical Society, 2017
HE0450-2958, an interacting quasar-starburst galaxy pair at z = 0.285, is one of the bestknown ex... more HE0450-2958, an interacting quasar-starburst galaxy pair at z = 0.285, is one of the bestknown examples of strong star formation activity in the presence of a quasar-driven jet. We present new multiband Karl G. Jansky Very Large Array-imaging covering 1-6 GHz and reaching an angular resolution of up to 0.6 arcsec (a sixfold improvement over existing radio data). We confirm the previous detection of a spatially extended radio component around the quasar, indicating that there is ongoing star formation activity in the quasar host galaxy. For the first time, we directly detect a jet-like bipolar outflow from the quasar aligned with its companion star-forming galaxy (SFG) and several blobs of ionized gas in its vicinity identified in previous studies. Within the companion SFG, we find evidence for a flattening of the synchrotron spectral index towards the point of intersection with the jet axis, further suggesting that the outflow may actually be impacting its interstellar medium. We discuss two possible mechanisms that could have triggered the starburst in the companion SFG: a wet-dry merger with the quasar and jet-induced star formation. While triggering through interaction-driven gas dynamics cannot be excluded with current data, our new observations make HE0450-2958 a strong candidate for jet-induced star formation, and one of the rare links between local systems (like Minkowski's Object or Centaurus A) and the high-z regime where radio-optical alignments suggest that this phenomenon could be more common.
Monthly Notices of the Royal Astronomical Society, 2017
This document is made available in accordance with publisher policies and may differ from the pub... more This document is made available in accordance with publisher policies and may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the URL above for details on accessing the published version.
Monthly Notices of the Royal Astronomical Society, 2016
We investigate the multiplicity of extragalactic sources detected by the Herschel Space Observato... more We investigate the multiplicity of extragalactic sources detected by the Herschel Space Observatory in the COSMOS field. Using 3.6-and 24-µm catalogues, in conjunction with 250-µm data from Herschel, we seek to determine if a significant fraction of Herschel sources are composed of multiple components emitting at 250 µm. We use the XID+ code, using Bayesian inference methods to produce probability distributions of the possible contributions to the observed 250-µm flux for each potential component. The fraction of Herschel flux assigned to the brightest component is highest for sources with total 250-µm fluxes <45 mJy; however, the flux in the brightest component is still highest in the brightest Herschel sources. The faintest 250-µm sources (30-45 mJy) have the majority of their flux assigned to a single bright component; the second brightest component is typically significantly weaker, and contains the remainder of the 250-µm source flux. At the highest 250-µm fluxes (45-110 mJy), the brightest and second brightest components are assigned roughly equal fluxes, and together are insufficient to reach 100 per cent of the 250-µm source flux. This indicates that additional components are required, beyond the brightest two components, to reproduce the observed flux. 95 per cent of the sources in our sample have a second component that contains more than 10 per cent of the total source flux. Particularly for the brightest Herschel sources, assigning the total flux to a single source may overestimate the flux contributed by around 150 per cent.
The Astrophysical Journal, 2015
Local starbursts have a higher efficiency of converting gas into stars, as compared to typical st... more Local starbursts have a higher efficiency of converting gas into stars, as compared to typical starforming galaxies at a given stellar mass, possibly indicative of different modes of star formation. With the peak epoch of galaxy formation occurring at z > 1, it remains to be established whether such an efficient mode of star formation is occurring at high-redshift. To address this issue, we measure the molecular gas content of seven high-redshift (z ∼ 1.6) starburst galaxies with the Atacama Large (sub-)Millimeter Array and IRAM/Plateau de Bure Interferometer. Our targets are selected from the sample of Herschel far-infrared detected galaxies having star formation rates (∼300-800 M ⊙ yr -1 ) elevated ( 4×) above the star-forming 'main sequence', and included in the FMOS-COSMOS nearinfrared spectroscopic survey of star-forming galaxies at z ∼ 1.6 with Subaru. We detect CO emission in all cases at high levels of significance, indicative of high gas fractions (∼30-50%). Even more compelling, we firmly establish with a clean and systematic selection that starbursts, identified as main-sequence outliers, at high redshift generally have a lower ratio of CO to total infrared luminosity as compared to typical main-sequence star-forming galaxies, although with a smaller offset than expected based on past studies of local starbursts. We put forward a hypothesis that there exists a continuous increase in star formation efficiency with elevation from the main sequence with galaxy mergers as a possible physical driver. Along with a heightened star formation efficiency, our highredshift sample is similar in other respects to local starbursts such as being metal rich and having a higher ionization state of the interstellar medium.
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Papers by Mark T . Sargent