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

## TL;DR

This study uses near-infrared spectroscopy to analyze five ultra-massive galaxies at redshifts 1.7 to 2.7, confirming their high stellar masses and diverse star formation activities through spectroscopic and photometric data.

## Contribution

First near-infrared spectroscopic analysis of ultra-massive galaxies at these redshifts, combining spectroscopy with photometry to refine stellar population properties.

## Key findings

- Three galaxies are quiescent with low star formation rates.
- One galaxy shows high star formation and dust obscuration.
- Spectroscopic data confirms extreme stellar masses.

## Abstract

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.