Engineering topics

Nair, Preethi

Publications and source records attributed to Nair, Preethi.

4 records

DOE OSTI2023

Post-starburst properties of post-merger galaxies

Post-starburst galaxies (PSBs) are transition galaxies showing evidence of recent rapid star formation quenching. To understand the role of galaxy mergers in triggering quenching, we investigate the incidence of PSBs and resolved PSB properties in post-merger galaxies using both SDSS single-fibre spectra and MaNGA resolved IFU spectra. We find post-mergers have a PSB excess of 10–20 times that relative to their control galaxies using single-fibre PSB diagnostics. A similar excess of ∼ 19 times is also found in the fraction of central (C)PSBs and ring-like (R)PSBs in post-mergers using the resolved PSB diagnostic. However, 60 per cent of the CPSBs + RPSBs in both post-mergers and control galaxies are missed by the single-fibre data. By visually inspecting the resolved PSB distribution, we find that the fraction of outside-in quenching is seven times higher than inside-out quenching in PSBs in post-mergers while PSBs in control galaxies do not show large differences in these quenching directions. In addition, we find a marginal deficit of HI gas in PSBs relative to non-PSBs in post-mergers using the MaNGA-HI data. The excesses of PSBs in post-mergers suggest that mergers play an important role in triggering quenching. Resolved IFU spectra are important to recover the PSBs missed by single-fibre spectra. The excess of outside-in quenching relative to inside-out quenching in post-mergers suggests that AGNs are not the dominant quenching mechanism in these galaxies, but that processes from the disc (gas inflows/consumption and stellar feedback) play a more important role.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2023

A Multiwavelength Study of Active Galactic Nuclei in Post-merger Remnants

Here, we investigate the role of galaxy mergers in triggering active galactic nuclei (AGN) in the nearby universe. Our analysis is based on a sample of 79 post-merger remnant galaxies with deep X-ray observations from Chandra/XMM-Newton capable of detecting a low-luminosity AGN of ≥10 40.5 erg s -1 . This sample is derived from a visually classified, volume-limited sample of 807 post-mergers identified in the Sloan Digital Sky Survey Data Release 14 with log M * /M ⊙ ≥ 10.5 and 0.02 ≤ z ≤ 0.06. We find that the X-ray AGN fraction in this sample is 55.7% ± 5.6% compared to 23.6% ± 2.8% for a mass- and redshift-matched noninteracting control sample. The multiwavelength AGN fraction (identified as an AGN in one of X-ray, IR, radio or optical diagnostics) for post-mergers is 76.6% ± 4.8% compared to 39.1% ± 3.2% for controls. Thus post-mergers exhibit a high overall AGN fraction with an excess between 2 and 4 depending on the AGN diagnostics used. In addition, we find most optical, IR, and radio AGN are also identified as X-ray AGN while a large fraction of X-ray AGN are not identified in any other diagnostic. This highlights the importance of deep X-ray imaging to identify AGN. We find that the X-ray AGN fraction of post-mergers is independent of the stellar mass above log M * /M ⊙ ≥ 10.5 unlike the trend seen in control galaxies. Overall, our results show that post-merger galaxies are a good tracer of the merger–AGN connection and strongly support the theoretical expectations that mergers trigger AGN.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

Resolved Molecular Gas Observations of MaNGA Post-starbursts Reveal a Tumultuous Past

Post-starburst (PSB) galaxies have recently and rapidly quenched their star formation; thus, they are an important way to understand how galaxies transition from star-forming late types to quiescent early types. The recent discovery of large cold gas reservoirs in PSB galaxies calls into question the theory that galaxies must lose their gas to become quiescent. Optical Integral Field Spectroscopy (IFS) surveys have revealed two classes of PSB galaxies: central PSB (cPSB) galaxies with central quenching regions and ring PSB (rPSB) galaxies with quenching in their outskirts. We analyze a sample of 13 nearby (z < 0.1) PSB galaxies with spatially resolved optical IFS data from the Mapping Nearby Galaxies at Apache Point Observatory survey and matched resolution Atacama Large Millimeter/submillimeter Array observations of 12 CO(1–0). Disturbed stellar kinematics in 7/13 of our PSB galaxies and centrally concentrated molecular gas is consistent with a recent merger for most of our sample. In galaxies without merger evidence, alternate processes may funnel gas inward and suppress star formation, which may include outflows, stellar bars, and minor mergers or interactions. The star formation efficiencies of the PSB regions in nearly half our galaxies are suppressed while the gas fractions are consistent with star-forming galaxies. Active galactic nucleus (AGN) feedback may drive this stabilization, and we observe AGN-consistent emission in the centers of 5/13 galaxies. Finally, our cPSB and rPSB galaxies have similar properties except the ionized and molecular gas in cPSB galaxies is more disturbed. Overall, the molecular gas in our PSB galaxies tends to be compact and highly disturbed, resulting in concentrated gas reservoirs unable to form stars efficiently.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Signatures of Inflowing Gas in Red Geyser Galaxies Hosting Radio Active Galactic Nuclei

We study cool neutral gas traced by NaD absorption in 140 local ($z$ < 0.1) early-type red geyser galaxies. These galaxies show unique signatures in spatially resolved strong line emission maps that have been interpreted as largescale active galactic nucleus–driven ionized winds. To investigate the possible fuel source for these winds, we examine the abundance and kinematics of cool gas ($T$ ~ 100–1000 K) inferred from Na I D absorption in red geysers and matched control samples drawn from the Sloan Digital Sky Survey IV Mapping Nearby Galaxies at Apache Point Observatory survey. We find that red geysers host greater amounts of NaD-associated material. Substantial cool gas components are detected in more than 50% of red geysers (compared to 25% of the control sample) going up to 78% for radio-detected red geysers. Our key result is that cool gas in red geysers is predominantly infalling. Among our 30 radio-detected red geysers, 86% show receding NaD absorption velocities (with respect to the systemic velocity) between 40 and 50 km s-1 . We verify this result by stacking NaD profiles across each sample, which confirms the presence of infalling NaD velocities within red geysers (~40 km s -1 ) with no velocity offsets detected in the control samples. Interpreting our observations as signatures of inflowing cool neutral clouds, we derive an approximate mass inflow rate of $\dot{M}$ in ~ 0.1$M$ ⊙ yr -1 , similar to that expected from minor merging and internal recycling. In conclusion, some red geysers show much higher rates ($\dot{M}$ in ~ 5$M$ ⊙ yr -1 ), which may indicate an ongoing accretion event.

79 ASTRONOMY AND ASTROPHYSICS↗