arXiv subjects

S. J. McKay

Publications and source records attributed to S. J. McKay.

4 recordsLinked to original sources

arXiv2026

A Deep ALMA Survey of the Redshift Distribution of Dusty Star-forming Galaxies

We present an Atacama Large Millimeter/submillimeter Array (ALMA) spectroscopic follow-up survey of an 870 $μ$m-selected sample of dusty star-forming galaxies (DSFGs) in the GOODS-S field. We use these linescans to identify or confirm spectroscopic redshifts (spec-zs) for 26 sources. Including spec-zs from the literature, there are now secure or tentative spec-zs for 54 out of 75 DSFGs (72%). At $f_{870}>2.5$ mJy, the sample is 97% spectroscopically complete, allowing us to model the full DSFG redshift distribution down to nearly the confusion limit for a 15-m telescope at 850 $μ$m. This is the highest completeness for an unbiased sample at this flux limit to date. We find that nearly all of the DSFGs in our sample that were targeted with JWST/NIRSpec were spectroscopically identified, without much dependence on near-infrared or submillimeter flux or redshift. However, only 29% of our sample have JWST spectroscopic coverage. We use the spec-zs to evaluate various photometric redshift (photo-z) estimates, finding that all methods exhibit an outlier fraction of at least $>20$%. Nearly all of the photo-z methods tend to overshoot the redshifts, leading to overestimates of the number of DSFGs at high redshift ($z>4$). Our results suggest that $\lesssim6$% of $f_{870} \geq 2.25$ mJy DSFGs lie at $z>4$ and $\lesssim1$% lie at $z>5$, reflecting a steep decline in the abundance of massive dusty galaxies in the first 1.5 Gyr.

astro-ph.GA↗

arXiv2026

A Redshift-based Red Selection of Dusty Star-forming Galaxies

We use JWST observations (1.5 micron to 4.44 micron), together with complete ALMA observations (870 micron and/or 1.2 mm), of the massive lensing cluster field A2744 to show that galaxies between z=1.5 and z=5.5 with rest-frame red colors f_J/f_V > 3 correspond to dusty star-forming galaxies (DSFGs), little red dots (LRDs), and quiescent galaxies. The color selection picks out 34 of the 41 >4.5-sigma ALMA sources in the field (83%). We find that the luminous red sources are generally extended, while the less luminous red sources are almost all compact and correspond to the LRD population. We also find that the great majority of the luminous, extended red sources are DSFGs based on the ALMA data, with a small admixture of quiescent galaxies at z<3-4 that we identify based on their location in the rest-frame U-V versus V-J diagram. We do not detect any LRDs or quiescent galaxies at the >3-sigma level in the ALMA images. Roughly 10% of the DSFGs have high rest-frame X-ray luminosities and must be AGN dominated. The DSFGs and quiescent galaxies nearly all have M_star>10^{10} solar masses. These massive galaxies become rare at z>5, paralleling the fall off in the number of detected DSFGs.

astro-ph.GA↗

arXiv2024

Comparing SCUBA-2 and ALMA Selections of Faint DSFGs in Abell 2744

We make a comparison of deep SCUBA-2 450 $μ$m and 850 $μ$m imaging on the massive lensing cluster field Abell 2744 with Atacama Large Millimeter/submillimeter Array (ALMA) 1.2 mm data. Our primary goal is to assess how effective the wider-field SCUBA-2 sample, in combination with red JWST priors, is for finding faint dusty star-forming galaxies (DSFGs) compared to the much more expensive mosaicked ALMA observations. We cross-match our previously reported direct ($>5σ$) SCUBA-2 sample and red JWST NIRCam prior-selected ($>3σ$) SCUBA-2 sample to direct ALMA sources from the DUALZ survey. We find that roughly 95% are confirmed by ALMA. The red priors also allow us to probe deeper in the ALMA image. Next, by measuring the 450 $μ$m and 850 $μ$m properties of the full ALMA sample, we show that 46/69 of the ALMA sources are detected at 850 $μ$m and 24/69 are detected at 450 $μ$m in the SCUBA-2 images, with a total detection fraction of nearly 75%. All of the robust ($>5σ$) ALMA sources that are not detected in at least one SCUBA-2 band lie at 1.2 mm fluxes $\lesssim$ 0.6 mJy and are undetected primarily due to the higher SCUBA-2 flux limits. We also find that the SCUBA-2 detection fraction drops slightly beyond $z=3$, which we attribute to the increasing 1.2 mm to 850 $μ$m and 1.2 mm to 450 $μ$m flux ratios combined with the ALMA selection. The results emphasize the power of combining SCUBA-2 data with JWST colors to map the faint DSFG population.

astro-ph.GA↗

arXiv2023

Dust Properties of 870 Micron Selected Galaxies in the GOODS-S

We analyze the dust properties of 57 870 $μ$m selected dusty star-forming galaxies in the GOODS-S using new deep ALMA 1.2 mm, 2 mm, and 3 mm continuum imaging together with other far-infrared through millimeter data. We fit the spectral energy distributions (SEDs) with optically thin modified blackbodies to constrain the emissivity indices and effective dust temperatures, finding a median emissivity index of $β= 1.78^{+0.43}_{-0.25}$ and a median temperature of $T_d = 33.6^{+12.1}_{-5.4}$ K. We observe a negative correlation between $β$ and $T_d$. By testing several SED models, we determine that the derived emissivity indices can be influenced by opacity assumptions. Our temperature measurements are consistent with no evolution in dust temperature with redshift.

astro-ph.GA↗