Not-so-little Red Dots: Two massive and dusty starbursts at z~5-7 pushing the limits of star formation discovered by JWST in the COSMOS-Web survey
We present the properties of two candidate massive ($M_\star\sim10^{11}M_\odot$) and dusty ($A_{\rm v}>2.5$ mag) galaxies at $z=5-7$ in the first 0.28 deg$^2$ of the COSMOS-Web survey. One object is spectroscopically confirmed at $z_{\rm spec}=5.051$, while the other has a robust $z_{\rm phot}=6.7\pm0.3$. Thanks to their extremely red colors ($F277W-F444W\sim1.7$ mag), these galaxies satisfy the nominal color-selection for the widely-studied ``little red dot" (LRD) population with the exception of their spatially-resolved morphologies. The morphology of our targets allows us to conclude that their red continuum is dominated by highly obscured stellar emission and not by reddened nuclear activity. Using a variety of SED-fitting tools and star formation histories, we estimate the stellar masses to be $\log(M_\star)=11.32^{+0.07}_{-0.15}$ $M_\odot$ and $\log(M_\star)=11.2^{+0.1}_{-0.2}$ $M_\odot$, respectively, with a red continuum emission dominated by a recent episode of star formation. We then compare their number density to the halo mass function to infer stellar baryon fractions of $ε_\star\sim0.25$ and $ε_\star\sim0.5$. Both are significantly higher than what is commonly observed in lower-z galaxies or more dust-obscured galaxies at similar redshifts. With very bright ultra-high-z Lyman-Break Galaxies and some non-AGN dominated LRDs, such ``extended" LRDs represent another population that may require very efficient star formation at early times.
Authors
- Louise Paquereau (ORCID: https://orcid.org/0000-0003-2397-0360)
- Jed McKinney (ORCID: https://orcid.org/0000-0002-6149-8178)
- Santosh Harish (ORCID: https://orcid.org/0000-0003-0129-2079)
- Marko Shuntov (ORCID: https://orcid.org/0000-0002-7087-0701)
- Hollis B. Akins (ORCID: https://orcid.org/0000-0003-3596-8794)
- G. Gozaliasl (ORCID: https://orcid.org/0000-0002-0236-919X)
- Vasily Kokorev (ORCID: https://orcid.org/0000-0002-5588-9156)
- H. J. McCracken (ORCID: https://orcid.org/0000-0002-9489-7765)
- E. Berman (ORCID: https://orcid.org/0000-0002-8494-3123)
- Nicole E. Drakos (ORCID: https://orcid.org/0000-0003-4761-2197)
- Anton M. Koekemoer (ORCID: https://orcid.org/0000-0002-6610-2048)
- R. Michael Rich (ORCID: https://orcid.org/0000-0003-0427-8387)
- Caitlin M. Casey (ORCID: https://orcid.org/0000-0002-0930-6466)
- O. Ilbert (ORCID: https://orcid.org/0000-0002-7303-4397)
- G. Magdis (ORCID: https://orcid.org/0000-0002-4872-2294)
- Olivia R. Cooper (ORCID: https://orcid.org/0000-0003-3881-1397)
- Fabrizio Gentile (ORCID: https://orcid.org/0000-0002-8008-9871)
- Maximilien Franco (ORCID: https://orcid.org/0000-0002-3560-8599)
- Jason Rhodes (ORCID: https://orcid.org/0000-0002-4485-8549)
- Brant E. Robertson (ORCID: https://orcid.org/0000-0002-4271-0364)
- Arianna S. Long (ORCID: https://orcid.org/0000-0002-7530-8857)
- Sune Toft (ORCID: https://orcid.org/0000-0003-3631-7176)
- Jeyhan S. Kartaltepe (ORCID: https://orcid.org/0000-0001-9187-3605)
- Daizhong Liu (ORCID: https://orcid.org/0000-0001-9773-7479)
- M. Talia (ORCID: https://orcid.org/0000-0003-4352-2063)
- Michaela Hirschmann (ORCID: https://orcid.org/0000-0002-3301-3321)
- Natalie Allen (ORCID: https://orcid.org/0000-0001-9610-7950)
Institutions
- University of Copenhagen (DK)
Publication Details
- Journal
- arXiv (Cornell University)
- Published
- 2024-08-19
- DOI
- https://doi.org/10.48550/arxiv.2408.10305
- Primary Topic
- Astronomy and Astrophysical Research
- Type
- article