Abstract
We investigate a sample of 152 dusty sources at 1.5 < z < 2.5 to understand the connection of enhanced star formation rate (SFR) and black hole accretion rate. The sources are Herschel-selected, having stellar masses M * > 1010 M ⊙ and SFR (~100–1000 M ⊙ yr−1) elevated (>4×)
above the star-forming "main sequence," classifying them as starbursts
(SBs). Through a multiwavelength fitting approach (including a dusty
torus component), we divided the sample into active SBs (dominated by an
active galactic nucleus (AGN) emission, SBs-AGN, ~23% of the sample)
and purely star-forming SBs (SBs-SFR). We visually inspected their Hubble Space Telescope/ultraviolet
(UV) rest frame maps: SBs-SFR are generally irregular and composite
systems; ~50% of SBs-AGN are instead dominated by regular compact
morphologies. We then found archival Atacama Large
Millimeter/submillimeter Array continuum counterparts for 33 galaxies
(12 SBs-AGN and 21 SBs-SFR). For these sources we computed dust masses,
and, with standard assumptions, we also guessed total molecular gas
masses. SBs turn into gas-rich systems (f gas = M gas/(M gas + M *) 20%–70%), and the gas fractions of the two SB classes are very similar (f gas = 43% ± 4% and f gas
= 42% ± 2%). Our results show that SBs are consistent with a mixture
of: (1) highly star-forming merging systems (dominating the SBs-SFR) and
(2) primordial galaxies, rapidly growing their M * together with their black hole (mainly the more compact SBs-AGN). Feedback effects have not yet reduced their f gas. Indeed, SBs at z = 2, with relatively low bolometric AGN luminosities in the range 1044 < L bol(AGN) < 1046 erg s−1
(compared to bright optical and X-ray quasars), are still relatively
far from the epoch when the AGN feedback will quench the SFR in the host
and will substantially depress the gas fractions.
Original language | English |
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Article number | L38 |
Journal | Astrophysical Journal Letters |
Volume | 877 |
Issue number | 2 |
Number of pages | 7 |
ISSN | 2041-8205 |
DOIs | |
Publication status | Published - 2019 |
Keywords
- Galaxies: active
- Galaxies: evolution
- Galaxies: formation
- Galaxies: high-redshift
- Galaxies: starburst
- Infrared: galaxies