arXiv subjects

Erin Kado-Fong

Publications and source records attributed to Erin Kado-Fong.

40 records · Page 3Linked to original sources

arXiv2017

A spectroscopic follow-up program of very massive galaxies at 3<z<4: confirmation of spectroscopic redshifts, and a high fraction of powerful AGN

We present the analysis and results of a spectroscopic follow-up program of a mass-selected sample of six galaxies at 3 < z < 4 using data from Keck-NIRSPEC and VLT-Xshooter. We confirm the z > 3 redshifts for half of the sample through the detection of strong nebular emission lines, and improve the zphot accuracy for the remainder of the sample through the combination of photometry and spectra. The modeling of the emission-line-corrected spectral energy distributions (SEDs) adopting improved redshifts confirms the very large stellar masses of the sample (M_* ~ 1.5-4 x 10^11 Msun) in the first 2 Gyrs of cosmic history, with a diverse range in stellar ages, star formation rates and dust content. From the analysis of emission line luminosities and widths, and far-infrared (FIR) fluxes we confirm that >80% of the sample are hosts to luminous hidden active galactic nuclei (AGNs), with bolometric luminosities of ~10^(44-46) erg/s. We find that the MIPS 24um photometry is largely contaminated by AGN continuum, rendering the SFRs derived using only 24um photometry to be severely overestimated. By including the emission from the AGN in the modeling of the UV-to-FIR SEDs, we confirm that the presence of the AGN does not bias considerably the stellar masses (< 0.3 dex at 1σ). We show evidence for a rapid increase of the AGN fraction from ~30% to ~60-100% over the 1 Gyr between z~2 and z~3. Although we cannot exclude some enhancement of the AGN fraction for our sample due to selection effects, the small measured [OIII] contamination to the observed K-band fluxes suggests that our sample is not significantly biased toward massive galaxies hosting AGNs.

astro-ph.GA↗

arXiv2017

Early Science with the Large Millimeter Telescope: Detection of dust emission in multiple images of a normal galaxy at $z>4$ lensed by a Frontier Fields cluster

We directly detect dust emission in an optically-detected, multiply-imaged galaxy lensed by the Frontier Fields cluster MACSJ0717.5+3745. We detect two images of the same galaxy at 1.1mm with the AzTEC camera on the Large Millimeter Telescope leaving no ambiguity in the counterpart identification. This galaxy, MACS071_Az9, is at z>4 and the strong lensing model (mu=7.5) allows us to calculate an intrinsic IR luminosity of 9.7e10 Lsun and an obscured star formation rate of 14.6 +/- 4.5 Msun/yr. The unobscured star formation rate from the UV is only 4.1 +/- 0.3 Msun/yr which means the total star formation rate (18.7 +/- 4.5 Msun/yr) is dominated (75-80%) by the obscured component. With an intrinsic stellar mass of only 6.9e9Msun, MACS0717_Az9 is one of only a handful of z>4 galaxies at these lower masses that is detected in dust emission. This galaxy lies close to the estimated star formation sequence at this epoch. However, it does not lie on the dust obscuration relation (IRX-beta) for local starburst galaxies and is instead consistent with the Small Magellanic Cloud (SMC) attenuation law. This remarkable lower mass galaxy showing signs of both low metallicity and high dust content may challenge our picture of dust production in the early Universe.

astro-ph.GA↗

arXiv2017

Near-infrared spectroscopy of 5 ultra-massive galaxies at 1.7 < z < 2.7

We present the results of a pilot near-infrared (NIR) spectroscopic campaign of five very massive galaxies ($\log(\text{M}_\star/\text{M}_\odot)>11.45$) in the range of $1.7<z<2.7$. We measure an absorption feature redshift for one galaxy at $z_\text{spec}=2.000\pm0.006$. For the remaining galaxies, we combine the photometry with the continuum from the spectra to estimate continuum redshifts and stellar population properties. We define a continuum redshift ($z_{\rm cont}$ ) as one in which the redshift is estimated probabilistically using EAZY from the combination of catalog photometry and the observed spectrum. We derive the uncertainties on the stellar population synthesis properties using a Monte Carlo simulation and examine the correlations between the parameters with and without the use of the spectrum in the modeling of the spectral energy distributions (SEDs). The spectroscopic constraints confirm the extreme stellar masses of the galaxies in our sample. We find that three out of five galaxies are quiescent (star formation rate of $\lesssim 1 M_\odot~yr^{-1}$) with low levels of dust obscuration ($A_{\rm V} < 1$) , that one galaxy displays both high levels of star formation and dust obscuration (${\rm SFR} \approx 300 M_\odot~{\rm yr}^{-1}$, $A_{\rm V} \approx 1.7$~mag), and that the remaining galaxy has properties that are intermediate between the quiescent and star-forming populations.

astro-ph.GA↗

arXiv2016

M Dwarf Activity in the Pan-STARRS 1 Medium-Deep Survey: First Catalog and Rotation Periods

We report on an ongoing project to investigate activity in the M dwarf stellar population observed by the Pan-STARRS 1 Medium Deep Survey (PS1-MDS). Using a custom-built pipeline, we refine an initial sample of $\approx$ 4 million sources in PS1-MDS to a sample of 184,148 candidate cool stars using color cuts. Motivated by the well-known relationship between rotation and stellar activity, we use a multi-band periodogram analysis and visual vetting to identify 271 sources that are likely rotating M dwarfs. We derive a new set of polynomials relating M dwarf PS1 colors to fundamental stellar parameters and use them to estimate the masses, distances, effective temperatures, and bolometric luminosities of our sample. We present a catalog containing these values, our measured rotation periods, and cross-matches to other surveys. Our final sample spans periods of $\lesssim$1-130 days in stars with estimated effective temperatures of $\approx$ 2700-4000 K. Twenty-two of our sources have X-ray cross-matches, and they are found to be relatively X-ray bright as would be expected from selection effects. Our data set provides evidence that Kepler-based searches have not been sensitive to very slowly-rotating stars ($P_{\rm rot} \gtrsim 70$ d), implying that the observed emergence of very slow rotators in studies of low-mass stars may be a systematic effect. We also see a lack of low-amplitude ($<$2%) variability in objects with intermediate (10-40 d) rotation periods, which, considered in conjunction with other observational results, may be a signpost of a loss of magnetic complexity associated with a phase of rapid spin-down in intermediate-age M dwarfs. This work represents just a first step in exploring stellar variability in data from the PS1-MDS and, in the farther future, LSST.

astro-ph.SR↗