arXiv subjects

D. A. Riechers

Publications and source records attributed to D. A. Riechers.

At least 19 recordsLinked to original sources

arXiv2026

Resolved SED modelling with JWST and ALMA: the role of stellar mass surface density in regulating star formation in cosmic noon galaxies

We present kpc-scale ($0.2''-0.5''$) physical property maps of 35 main-sequence galaxies at $z \approx 0.5-3.7$, with stellar masses of $\log(M_*/M_\odot) \sim 9.7-11.7$ and star formation rates of $\mathrm{SFR} \sim 1.4-280\,\mathrm{M_\odot\,yr^{-1}}$, selected from the ALMA Spectroscopic Survey (ASPECS) in the Hubble Ultra Deep Field. Leveraging the unique HST, JWST (NIRCam and MIRI), and ALMA observations, we perform spatially resolved spectral energy distribution (SED) modeling across the UV-to-FIR regime. We find that incorporating MIRI and/or ALMA data reduces the overestimation of dust luminosity (by up to $\sim0.8$ dex), while ALMA observations further mitigate the age-dust degeneracy. In the absence of such data, restricting the SED model library based on the observed unresolved colors can partially mitigate these biases. The stellar masses ($M_{*}$) derived from resolved and unresolved modeling are consistent within $\sim0.05$ dex, suggesting that mass discrepancies (attributed to outshining) are less significant for cosmic noon main-sequence galaxies when rest-frame near-infrared (NIR; e.g., $\sim1-3\,μ\mathrm{m}$) data are included. After normalization to the same reference, the composite SED of our sample closely resembles that of local starburst galaxies such as M82, suggesting similar dust attenuation and re-emission properties. Finally, we find that the molecular gas fraction and depletion time correlate with the effective stellar mass surface density ($Σ_{\rm eff,*} = M_{*}/2πR_{\rm eff,M_*}^2$) similarly to that observed in local galaxies. These results provide a first qualitative view of how the stellar gravitational potential influences gas regulation and star formation in galaxies beyond the local Universe.

astro-ph.GA↗

arXiv2026

Space as a spectroscopic laboratory: High-resolution spectroscopy of the [$^{13}$C II] hyperfine structure with SOFIA/upGREAT

The [$^{12}$C II] emission at 158 $μ$m is a key cooling line of the interstellar medium and traces gas kinematics in spectrally resolved observations. Its spectral profile is often modified by optical depth effects. The intrinsic line shape can be reconstructed by comparison with emission from the less abundant $^{13}$C isotope. Due to the additional neutron spin, [$^{13}$C II] emission splits into three hyperfine structure (hfs) transitions. Laboratory measurements have provided the centroid frequency and the strongest component ($F=2-1$); the two weaker components ($F=1-0$ and $F=1-1$) have been inferred only from quantum-mechanical calculations. The magnetic-dipole hfs constants, from which the transition frequencies follow, have not been measured experimentally. The high spectral resolution of observations with the upgraded German Receiver for Astronomy at Terahertz Frequencies (upGREAT) on board SOFIA enabled simultaneous detection of all three hfs transitions. From these astronomical data we determine, for the first time, the magnetic-dipole hfs constants $A_{1/2}^{\rm hf} = 810.71(11)$ MHz and $A_{3/2}^{\rm hf} = 162.18(5)$ MHz of the [$^{13}$C II] $2s^2\,2p\,{}^2P^\circ$ ground term. Combined with the laboratory centroid frequency, this yields the rest frequencies of all three hfs lines. Using [$^{12}$C II] as a reference, we also improve the precision of the [$^{13}$C II] centroid frequency. This work shows that spectrally resolved astronomical observations can constrain fundamental atomic properties, with hfs precision rivaling laboratory measurements. The approach extends to other atomic and molecular transitions where laboratory data are difficult to obtain.

astro-ph.GA↗

arXiv2025

The ALPINE-CRISTAL-JWST Survey: JWST/IFU Optical Observations for 18 Main-Sequence Galaxies at z=4-6

To fully characterize the formation and evolution of galaxies, we need to observe their stars, gas, and dust on resolved spatial scales. We present the ALPINE-CRISTAL-JWST survey, which combines kpc-resolved imaging and spectroscopy from HST, JWST, and ALMA for 18 representative main-sequence galaxies at z=4-6 and log(M/$M_\odot$) > 9.5 to study their star formation, chemical properties, and extended gas reservoirs. The co-spatial measurements resolving the ionized gas, molecular gas, stars, and dust on 1-2 kpc scales make this a unique benchmark sample for the study of galaxy formation and evolution at $z\sim5$, connecting the Epoch of Reionization with the cosmic noon. In this paper, we outline the survey goals and sample selection, and present a summary of the available data for the 18 galaxies. In addition, we measure spatially integrated quantities (such as global gas metallicity), test different star formation rate indicators, and quantify the presence of H$α$ halos. Our targeted galaxies are relatively metal rich (10-70% solar), complementary to JWST samples at lower stellar mass, and there is broad agreement between different star formation indicators. One galaxy has the signature of an active galactic nuclei (AGN) based on its emission line ratios. Six show broad H$α$~emission suggesting type 1 AGN candidates. We conclude with an outlook on the exciting science that will be pursued with this unique sample in forthcoming papers.

astro-ph.GA↗

arXiv2025

The dust emissivity index beta in infrared-bright galaxies at 1.5 < z < 4.2

We have measured the dust emissivity index beta for 21 infrared-bright sources (including several gravitationally lensed galaxies) at 1.5 < z < 4.2 using Atacama Large Millimeter/submillimeter Array (ALMA) 101-199 GHz data sampling the Rayleigh-Jeans side of the SED. These data are largely insensitive to temperature variations and therefore should provide robust measurements of beta. We obtain a mean beta of 2.2 with a standard deviation of 0.6 that is at the high end of the range of values that had previously been measured in many galactic and extragalactic sources. We find no systematic variation in beta versus redshift. We also demonstrate with a subset of our sources that these higher beta values have significant implications for modelling dust emission and in particular for calculating dust masses or the wavelength at which dust becomes optically thick.

astro-ph.GA↗

arXiv2024

A hidden active galactic nucleus powering bright [O III] nebulae in a protocluster at $z=4.5$ revealed by JWST

Galaxy protoclusters are sites of rapid growth, with a high density of massive galaxies driving elevated rates of star formation and accretion onto supermassive black holes. Here, we present new JWST/NIRSpec IFU observations of the J1000+0234 group at $z=4.54$, a dense region of a protocluster hosting a massive, dusty star forming galaxy (DSFG). The new data reveal two extended, high-equivalent-width (EW$_0>1000Å$) [O III] nebulae that appear at both sides of the DSFG along its minor axis (namely O3-N and O3-S). On one hand, the spectrum of O3-N shows a broad and blueshifted component with a full width at half maximum (FWHM) of 1300 km/s, suggesting an outflow origin. On the other hand, O3-S stretches over 8.6 kpc, and has a velocity gradient that spans 800 km/s, but shows no evidence of a broad component. However, both sources seem to be powered by an active galactic nucleus (AGN), so we classified them as extended emission-line regions (EELRs). The strongest evidence comes from the detection of the high-ionization [Ne V] $λ3427$ line toward O3-N, which paired with the lack of hard X-rays implies an obscuring column density above the Compton-thick regime. The [Ne V] line is not detected in O3-S, but we measure a He II $λ4687$/H$β$=0.25, which is well above the expectation for star formation. Despite the remarkable alignment of O3-N and O3-S with two radio sources, we do not find evidence of shocks from a radio jet that could be powering the EELRs. We interpret this as O3-S being externally irradiated by the AGN, akin to the famous Hanny's Voorwerp object in the local Universe. In addition, classical line ratio diagnostics (e.g., [O III]/H$β$ vs [N II]/H$α$) put the DSFG itself in the AGN region of the diagrams, and therefore suggest it to be the most probable AGN host. These results showcase the ability of JWST to unveil obscured AGN at high redshifts.

astro-ph.GA↗

arXiv2024

A Novel high-z submm Galaxy Efficient Line Survey in ALMA bands 3 through 8 -- An ANGELS Pilot

We use the Atacama Large sub/Millimetre Array (ALMA) to efficiently observe spectral lines across Bands 3, 4, 5, 6, 7, and 8 at high-resolution (0.5" - 0.1") for 16 bright southern Herschel sources at $1.5 < z < 4.2$. With only six and a half hours of observations, we reveal 66 spectral lines in 17 galaxies. These observations detect emission from CO (3-2) to CO(18-17), as well as atomic ([CI](1-0), (2-1), [OI] 145 $μ$m and [NII] 205 $μ$m) lines. Additional molecular lines are seen in emission (${\rm H_2O}$ and ${\rm H_2O^+}$) and absorption (OH$^+$ and CH$^+$). The morphologies based on dust continuum ranges from extended sources to strong lensed galaxies with magnifications between 2 and 30. CO line transitions indicate a diverse set of excitation conditions with a fraction of the sources ($\sim 35$%) showcasing dense, warm gas. The resolved gas to star-formation surface densities vary strongly per source, and suggest that the observed diversity of dusty star-forming galaxies could be a combination of lensed, compact dusty starbursts and extended, potentially-merging galaxies. The predicted gas depletion timescales are consistent with 100 Myr to 1 Gyr, but require efficient fueling from the extended gas reservoirs onto the more central starbursts, in line with the Doppler-shifted absorption lines that indicate inflowing gas for two out of six sources. This pilot paper explores a successful new method of observing spectral lines in large samples of galaxies, supports future studies of larger samples, and finds that the efficiency of this new observational method will be further improved with the planned ALMA Wideband Sensitivity Upgrade.

astro-ph.GA↗

arXiv2024

A Collection of German Science Interests in the Next Generation Very Large Array

The Next Generation Very Large Array (ngVLA) is a planned radio interferometer providing unprecedented sensitivity at wavelengths between 21 cm and 3 mm. Its 263 antenna element array will be spatially distributed across North America to enable both superb low surface brightness recovery and sub-milliarcsecond angular resolution imaging. The project was developed by the international astronomy community under the lead of the National Radio Astronomy Observatory (NRAO), and is anticipated to be built between 2027 and 2037. Two workshops have been held in 2022 and 2023 with the goal to discuss and consolidate the scientific interests in the ngVLA within the German astronomical community. This community paper constitutes a collection of 48 science ideas which the German community aims to pursue with the ngVLA in the 2030s. This is not a complete list and the ideas are not developed at the level of a "Science Book", such that the present document is mainly meant provide a basis for further discussion within the community. As such, additional contributions are welcome, and will be considered for inclusion in future revisions.

astro-ph.IM↗

arXiv2024

A dusty proto-cluster surrounding the binary galaxy HerBS-70 at $z = 2.3$

We report on deep SCUBA-2 observations at 850$μ$m and NOEMA spectroscopic measurements at 2 mm of the environment surrounding the luminous, massive ($M_{*} \approx 2 \times 10^{11}$ M$_{\odot}$) Herschel-selected source HerBS-70. This source was revealed by previous NOEMA observations to be a binary system of dusty star-forming galaxies at $z= 2.3$, with the East component (HerBS-70E) hosting an Active Galactic Nucleus (AGN). The SCUBA-2 observations detected, in addition to the binary system, twenty-one sources at $> 3.5 σ$ over an area of $\sim 25$ square comoving Mpc with a sensitivity of $σ_{850} = 0.75$ mJy. The surface density of continuum sources around HerBS-70 is three times higher than for field galaxies. The NOEMA spectroscopic measurements confirm the protocluster membership of three of the nine brightest sources through their CO(4 - 3) line emission, yielding a volume density 36 times higher than for field galaxies. All five confirmed sub-mm galaxies in the HerBS-70 system have relatively short gas depletion times ($80 - 500$ Myr), indicating the onset of quenching for this protocluster core due to the depletion of gas. The dark matter halo mass of the HerBS-70 system is estimated around $5 \times{} 10^{13}$ M$_{\odot}$, with a projected current-day mass of $10^{15}$ M$_{\odot}$, similar to the local Virgo and Coma clusters. These observations support the claim that DSFGs, in particular the ones with observed multiplicity, can trace cosmic overdensities.

astro-ph.GA↗

arXiv2023

NOEMA observations of GN-z11: Constraining Neutral Interstellar Medium and Dust Formation in the Heart of Cosmic Reionization at $z=10.6$

We present results of dust continuum and [CII]$\,158\,{\rm μm}$ emission line observations of a remarkably UV-luminous ($M_{\rm UV}=-21.6$) galaxy at $z=10.603$: GN-z11. Using the Northern Extended Millimeter Array (NOEMA), observations have been carried out over multiple observing cycles. We achieved a high sensitivity resulting in a $λ_{\rm rest}=160\,{\rm μm}$ continuum $1\,σ$ depth of $13.0\,\rm{μJy/beam}$ and a [CII] emission line $1\,σ$ sensitivity of $31\,\rm{mJy/beam\,km/s}$ using $50\,\rm{km/s}$ binning with a $\sim 2\,{\rm arcsec}$ synthesized beam. Neither dust continuum nor [CII]$\,158\,{\rm μm}$ line emission are detected at the expected frequency of $ν_{\rm [CII]} = 163.791\,\rm{GHz}$ and the sky location of GN-z11. The upper limits show that GN-z11 is neither luminous in $L_{\rm IR}$ nor $L_{\rm [CII]}$, with a dust mass $3\,σ$ limit of ${\rm log}(M_{\rm dust}/{\rm M_{\odot}}) < 6.5-6.9$ and with a [CII] based molecular gas mass $3\,σ$ limit of ${\rm log}(M_{\rm mol,[CII]}/{\rm M_{\odot}}) < 9.3$. Together with radiative transfer calculations, we also investigated the possible cause of the dust poor nature of the GN-z11 showed by the blue color in the UV continuum of GN-z11 ($β_{\rm UV}=-2.4$), and found that $\gtrsim3\times$ deeper observations are crucial to study dust production at very high-redshift. Nevertheless, our observations show the crucial role of deep mm/submm observations of very high redshift galaxies to constrain multiple phases in the interstellar medium.

astro-ph.GA↗

arXiv2023

z-GAL -- A NOEMA spectroscopic redshift survey of bright Herschel galaxies: [I] Overview

(Abridged) Using the IRAM NOEMA interferometer, we measures the redshifts of 126 bright galaxies detected in the Herschel H-ATLAS, HeLMS, and HerS surveys. We report reliable spectroscopic redshifts for a total of 124 of the Herschel-selected galaxies. The redshifts are estimated from scans of the 3 and 2-mm bands (and, in one case, the 1-mm band) and are based on the detection of at least two emission lines. Together with the Pilot Programme (Neri et al. 2020), including spectroscopic redshifts of 11 sources, our survey has derived precise redshifts for 135 bright Herschel-selected galaxies, making it the largest sample of high-z galaxies with robust redshifts to date. Most emission lines detected are from 12CO (mainly from J=2-1 to 5-4), with some sources seen in [CI] and H2O emission lines. The spectroscopic redshifts are in the range 0.8<z<6.55 with a median value of z=2.56 +/- 0.10. The line widths of the sources are large, with a mean value for the full width at half maximum Delta(V) of 590 +/- 25 km/s and with 35% of the sources having widths of 700 km/s < Delta(V) < 1800 km/s. Most of the sources are unresolved or barely resolved on scales of 2 to 3 arcsec (or linear sizes of 15-25 kpc, unlensed). Some fields reveal double or multiple sources and, in some cases, sources at different redshifts. Taking these sources into account, there are, in total, 165 individual sources with robust spectroscopic redshifts, including lensed galaxies, binary systems, and over-densities. We present an overview of the z-GAL survey and provide the observed properties of the emission lines, the derived spectroscopic redshifts, and an atlas of the entire sample. The data presented here will serve as a foundation for the other z-GAL papers in this series reporting on the dust emission, the molecular and atomic gas properties, and a detailed analysis of the nature of the sources.

astro-ph.GA↗

arXiv2023

z-GAL -- A NOEMA spectroscopic redshift survey of bright Herschel galaxies: [III] Physical properties

The z-GAL survey observed 137 bright Herschel-selected targets with the IRAM NOrthern Extended Millimeter Array, with the aim to measure their redshift and study their properties. Several of them have been resolved into multiple sources. Consequently, robust spectroscopic redshifts have been measured for 165 individual galaxies in the range 0.8<z<6.5. In this paper we analyse the millimetre spectra of the z-GAL sources, using both their continuum and line emission to derive their physical properties. At least two spectral lines are detected for each source, including transitions of 12CO, [CI], and H2O. The observed 12CO line ratios and spectral line energy distributions of individual sources resemble those of local starbursts. In seven sources the para-H2O(2_11-2_02) transition is detected and follows the IR versus H2O luminosity relation of sub-millimetre galaxies. The molecular gas mass of the z-GAL sources is derived from their 12CO, [CI], and sub-millimetre dust continuum emission. The three tracers lead to consistent results, with the dust continuum showing the largest scatter when compared to 12CO. The gas-to-dust mass ratio of these sources was computed by combining the information derived from 12CO and the dust continuum and has a median value of 107, similar to star-forming galaxies of near-solar metallicity. The same combined analysis leads to depletion timescales in the range between 0.1 and 1.0 Gyr, which place the z-GAL sources between the `main sequence' of star formation and the locus of starbursts. Finally, we derived a first estimate of stellar masses - modulo possible gravitational magnification - by inverting known gas scaling relations: the z-GAL sample is confirmed to be mostly composed by starbursts, whereas ~25% of its members lie on the main sequence of star-forming galaxies (within +/- 0.5 dex).

astro-ph.GA↗

arXiv2023

z-GAL -- A NOEMA spectroscopic redshift survey of bright Herschel galaxies: [II] Dust properties

(Abridged) We present the dust properties of 125 bright Herschel galaxies selected from the z-GAL survey. The large instantaneous bandwidth of NOEMA provides an exquisite sampling of the underlying dust continuum emission at 2 and 3 mm in the observed frame, with flux densities in at least four side bands for each source. Together with the available Herschel 250, 350, and 500 micron and SCUBA-2 850 micron flux densities, the spectral energy distribution of each source can be analyzed from the far-infrared to the millimeter, with a fine sampling of the Rayleigh-Jeans tail. This wealth of data provides a solid basis to derive robust dust properties, in particular the dust emissivity index, beta, and the dust temperature, T(dust). In order to demonstrate our ability to constrain the dust properties, we used a flux-generated mock catalog and analyzed the results under the assumption of an optically thin and optically thick modified black body emission. For the z-GAL sources, we report a range of dust emissivities with beta ~ 1.5 - 3 estimated up to high precision with relative uncertainties that vary in the range 7% - 15%, and an average of 2.2 +/- 0.3. We find dust temperatures varying from 20 to 50 K with an average of T(dust) ~ 30 K for the optically thin case and ~38 K in the optically thick case. For all the sources, we estimate the dust masses and apparent infrared luminosities (based on the optically thin approach). An inverse correlation is found between T(dust) and beta, which is similar to what is seen in the local Universe. Finally, we report an increasing trend in the dust temperature as a function of redshift at a rate of 6.5 +/- 0.5 K/z for this 500 micron-selected sample. Based on this study, future prospects are outlined to further explore the evolution of dust temperature across cosmic time.

astro-ph.GA↗

arXiv2023

The ALMA REBELS Survey: Discovery of a massive, highly star-forming and morphologically complex ULIRG at $z =7.31$

We present Atacama Large Millimeter/Submillimeter Array (ALMA) [CII] and $\sim158$ $\rmμm$ continuum observations of REBELS-25, a massive, morphologically complex ultra-luminous infrared galaxy (ULIRG; $L_{\rm IR}=1.5^{+0.8}_{-0.5}\times10^{12}$ L$_\odot$) at $z=7.31$, spectroscopically confirmed by the Reionization Era Bright Emission Line Survey (REBELS) ALMA Large Programme. REBELS-25 has a significant stellar mass of $M_{*}=8^{+4}_{-2}\times10^{9}$ M$_\odot$. From dust-continuum and ultraviolet observations, we determine a total obscured + unobscured star formation rate of SFR $=199^{+101}_{-63}$ M$_\odot$ yr$^{-1}$. This is about four times the SFR estimated from an extrapolated main-sequence. We also infer a [CII]-based molecular gas mass of $M_{\rm H_2}=5.1^{+5.1}_{-2.6}\times10^{10}$ $M_\odot$, implying a molecular gas depletion time of $ t_{\rm depl, H_2}=0.3^{+0.3}_{-0.2}$ Gyr. We observe a [CII] velocity gradient consistent with disc rotation, but given the current resolution we cannot rule out a more complex velocity structure such as a merger. The spectrum exhibits excess [CII] emission at large positive velocities ($\sim500$ km s$^{-1}$), which we interpret as either a merging companion or an outflow. In the outflow scenario, we derive a lower limit of the mass outflow rate of 200 M$_\odot$ yr$^{-1}$, which is consistent with expectations for a star formation-driven outflow. Given its large stellar mass, SFR and molecular gas reservoir $\sim700$ Myr after the Big Bang, we explore the future evolution of REBELS-25. Considering a simple, conservative model assuming an exponentially declining star formation history, constant star formation efficiency, and no additional gas inflow, we find that REBELS-25 has the potential to evolve into a galaxy consistent with the properties of high-mass quiescent galaxies recently observed at $z\sim4$.

astro-ph.GA↗

arXiv2023

Bright Extragalactic ALMA Redshift Survey (BEARS) III: Detailed study of emission lines from 71 Herschel targets

We analyse the molecular and atomic emission lines of 71 bright Herschel-selected galaxies between redshifts 1.4 to 4.6 detected by the Atacama Large Millimetre/submillimetre Array. These lines include a total of 156 CO, [C I], and H2O emission lines. For 46 galaxies, we detect two transitions of CO lines, and for these galaxies we find gas properties similar to those of other dusty star-forming galaxy (DSFG) samples. A comparison to photo-dissociation models suggests that most of Herschel-selected galaxies have similar interstellar medium conditions as local infrared-luminous galaxies and high-redshift DSFGs, although with denser gas and more intense far-ultraviolet radiation fields than normal star-forming galaxies. The line luminosities agree with the luminosity scaling relations across five orders of magnitude, although the star-formation and gas surface density distributions (i.e., Schmidt-Kennicutt relation) suggest a different star-formation phase in our galaxies (and other DSFGs) compared to local and low-redshift gas-rich, normal star-forming systems. The gas-to-dust ratios of these galaxies are similar to Milky Way values, with no apparent redshift evolution. Four of 46 sources appear to have CO line ratios in excess of the expected maximum (thermalized) profile, suggesting a rare phase in the evolution of DSFGs. Finally, we create a deep stacked spectrum over a wide rest-frame frequency (220-890 GHz) that reveals faint transitions from HCN and CH, in line with previous stacking experiments.

astro-ph.GA↗

arXiv2023

Resolved CO(1-0) emission and gas properties in luminous dusty star forming galaxies at z=2-4

We present the results of a survey of CO(1-0) emission in 14 infrared luminous dusty star forming galaxies (DSFGs) at 2 < z < 4 with the NSF's Karl G. Jansky Very Large Array. All sources are detected in CO(1-0), with an ~1arcsec angular resolution. Seven sources show extended and complex structure. We measure CO luminosities of $(μ)L'_{CO(1-0)}=0.4-2.9x10^{11}$ K km s$^{-1}$ pc$^2$, and molecular gas masses of ($μ$)M$_{H2}$ = 1.3 - 8.6 x 10$^{11}$ Mo, where (μ) is the magnification factor. The derived molecular gas depletion times of t$_{\rm dep}$ = 40 - 460 Myr, cover the expected range of both normal star forming galaxies and starbursts. Comparing to the higher-J CO transitions previously observed for the same sources, we find CO temperature brightness ratios of r$_{32/10}$ = 0.4 - 1.4, r$_{43/10}$ = 0.4 - 1.7, and r$_{54/10}$ = 0.3 - 1.3. We find a wide range of CO spectral line energy distributions (SLEDs), in agreement with other high-z DSFGs, with the exception of three sources that are most comparable to the Cloverleaf and APM08279+5255. Based on radiative transfer modelling of the CO SLEDs we determine densities of n$_{H2}$ = 0.3 - 8.5 x 10$^3$ cm$^{-3}$ and temperatures of T$_K$ = 100 - 200 K. Lastly, four sources are detected in the continuum, three have radio emission consistent with their infrared derived star formation rates, while HerBS-70E requires an additional synchrotron radiation component from an active galactic nucleus. Overall, we find that even though the sample is similarly luminous in the infrared, by tracing the CO(1-0) emission a diversity of galaxy and excitation properties are revealed, demonstrating the importance of CO(1-0) observations in combination to higher-J transitions.

astro-ph.GA↗

arXiv2023

The Bright Extragalactic ALMA Redshift Survey (BEARS) II: Millimetre photometry of gravitational lens candidates

We present 101 and 151 GHz ALMA continuum images for 85 fields selected from Herschel observations that have 500 micron flux densities >80 mJy and 250-500 micron colours consistent with z > 2, most of which are expected to be gravitationally lensed or hyperluminous infrared galaxies. Approximately half of the Herschel 500 micron sources were resolved into multiple ALMA sources, but 11 of the 15 brightest 500 micron Herschel sources correspond to individual ALMA sources. For the 37 fields containing either a single source with a spectroscopic redshift or two sources with the same spectroscopic redshift, we examined the colour temperatures and dust emissivity indices. The colour temperatures only vary weakly with redshift and are statistically consistent with no redshift-dependent temperature variations, which generally corresponds to results from other samples selected in far-infrared, submillimetre, or millimetre bands but not to results from samples selected in optical or near-infrared bands. The dust emissivity indices, with very few exceptions, are largely consistent with a value of 2. We also compared spectroscopic redshifts to photometric redshifts based on spectral energy distribution templates designed for infrared-bright high-redshift galaxies. While the templates systematically underestimate the redshifts by ~15%, the inclusion of ALMA data decreases the scatter in the predicted redshifts by a factor of ~2, illustrating the potential usefulness of these millimetre data for estimating photometric redshifts.

astro-ph.GA↗

arXiv2022

CCAT-prime Collaboration: Science Goals and Forecasts with Prime-Cam on the Fred Young Submillimeter Telescope

We present a detailed overview of the science goals and predictions for the Prime-Cam direct detection camera/spectrometer being constructed by the CCAT-prime collaboration for dedicated use on the Fred Young Submillimeter Telescope (FYST). The FYST is a wide-field, 6-m aperture submillimeter telescope being built (first light in mid-2024) by an international consortium of institutions led by Cornell University and sited at more than 5600 meters on Cerro Chajnantor in northern Chile. Prime-Cam is one of two instruments planned for FYST and will provide unprecedented spectroscopic and broadband measurement capabilities to address important astrophysical questions ranging from Big Bang cosmology through reionization and the formation of the first galaxies to star formation within our own Milky Way galaxy. Prime-Cam on the FYST will have a mapping speed that is over ten times greater than existing and near-term facilities for high-redshift science and broadband polarimetric imaging at frequencies above 300 GHz. We describe details of the science program enabled by this system and our preliminary survey strategies.

astro-ph.CO↗

arXiv2022

An ultra-deep multi-band VLA survey of the faint radio sky (COSMOS-XS): New constraints on the cosmic star formation history

We make use of ultra-deep 3 GHz Karl G. Jansky Very Large Array observations of the COSMOS field from the multi-band COSMOS-XS survey to infer radio luminosity functions (LFs) of star-forming galaxies (SFGs). Using $\sim$1300 SFGs with redshifts out to $z\sim4.6$, and fixing the faint and bright end shape of the radio LF to the local values, we find a strong redshift trend that can be fitted by pure luminosity evolution with the luminosity parameter given by $α_L \propto (3.40 \pm 0.11) - (0.48 \pm 0.06)z$. We then combine the ultra-deep COSMOS-XS data-set with the shallower VLA-COSMOS $\mathrm{3\,GHz}$ large project data-set over the wider COSMOS field in order to fit for joint density+luminosity evolution, finding evidence for significant density evolution. By comparing the radio LFs to the observed far-infrared (FIR) and ultraviolet (UV) LFs, we find evidence of a significant underestimation of the UV LF by $21.6\%\, \pm \, 14.3 \, \%$ at high redshift ($3.3\,<\,z\,<\,4.6$, integrated down to $0.03\,L^{\star}_{z=3}$). We derive the cosmic star formation rate density (SFRD) by integrating the fitted radio LFs and find that the SFRD rises up to $z\,\sim\,1.8$ and then declines more rapidly than previous radio-based estimates. A direct comparison between the radio SFRD and a recent UV-based SFRD, where we integrate both LFs down to a consistent limit ($0.038\,L^{\star}_{z=3}$), reveals that the discrepancy between the radio and UV LFs translates to a significant ($\sim$1 dex) discrepancy in the derived SFRD at $z>3$, even assuming the latest dust corrections and without accounting for optically dark sources.

astro-ph.GA↗