Understanding Galaxy Mergers & AGN Feedback with UVIT
K. Rubinur, M. Das, P. Kharb, Rahne P. T
备注：
3 pages, 2 figure, Poster presentation, Proceedings of the IAU356: Nuclear Activity in Galaxies across Cosmic Time, Addis Ababa, Ethiopia (7-11 October, 2019)
Simulations expect an enhanced star-formation and active galactic nuclei (AGN) activity during galaxy mergers, which can lead to formation of binary/dual AGN. AGN feedback can enhance or suppress star-formation. We have carried out a pilot study of a sample of 10 dual nuclei galaxies with AstroSat's Ultraviolet Imaging Telescope (UVIT). Here, we present the initial results for two sample galaxies (Mrk 739, ESO 509) and deep multi-wavelength data of another galaxy (Mrk 212). UVIT observations have revealed signatures of positive AGN feedback in Mrk 739 and Mrk 212, and negative feedback in ESO 509. Deeper UVIT observations have recently been approved; these will provide better constraints on star-formation as well as AGN feedback in these systems.
$\require{mediawiki-texvc}$ Supermassive black holes at the centre of active galactic nuclei (AGN) produce relativistic jets that can affect the star formation characteristics of the AGN hosts. Observations in the ultraviolet (UV) band can provide an excellent view of the effect of AGN jets on star formation. Here, we present a census of star formation properties in the Northern Star-forming Region (NSR) that spans about 20 kpc of the large radio source Centaurus A hosted by the giant elliptical galaxy NGC 5128. In this region, we identified 352 UV sources associated with Cen A using new obser…
An ultraviolet survey of M31 has been carried out during 2017-19 with the UVIT instrument onboard the AstroSat Observatory. Here we match the M31 UVIT source catalog (Leahy et al. 2020) with the Chandra source catalog (Vulic et al. 2016). We find 67 UVIT/Chandra sources detected in a varying number of UV and X-ray bands. The UV and X-ray photometry is analyzed using powerlaw and blackbody models. The X-ray types include 15 LMXBs and 5 AGNs. Cross-matches with catalogs of stars, clusters and other source types yield the following. 20 of the UVIT/Chandra sources match with M31 globular clusters …
Ultraviolet variability in Radio-Loud Active Galactic Nuclei observed by UVIT onboard AstroSat
CHRIST University（克里斯特大学）；Indian Institute of Astrophysics（印度天体物理研究所）；Center for Theoretical Physics of the Polish Academy of Sciences（波兰科学院理论物理中心）；St. Joseph’s University（圣约瑟夫大学）
We present imaging and photometric studies of the radio galaxy NGC 1316 (Fornax~A) using high spatial resolution near-ultraviolet (NUV) and far-ultraviolet (FUV) imaging telescopes of the first Indian multi-wavelength space observatory {\it AstroSat}. The residual maps of UV emission obtained from the subtraction of smooth models witness peculiar features within the central few kpc (1-2 kpc) region. The spatial correspondence between the radio emission maps and FUV imaging study reveal that the UV emitting sources are displaced away from the centre by the AGN outburst (radio jet). The presence…
Some post-merger galaxies are known to undergo a starburst phase that quickly depletes the gas reservoir and turns it into a red-sequence galaxy, though the details are still unclear. Here we explore the pattern of recent star formation in the central region of the post-merger galaxy NGC7252 using high resolution UV images from the UVIT on ASTROSAT. The UVIT images with 1.2 and 1.4 arcsec resolution in the FUV and NUV are used to construct a FUV-NUV colour map of the central region. The FUV-NUV pixel colour map for this canonical post-merger galaxy reveals a blue circumnuclear ring of diameter…
The question of whether galaxy mergers are linked to the triggering of active galactic nuclei (AGN) continues to be a topic of considerable debate. The issue can be broken down into two distinct questions: 1) Can galaxy mergers trigger AGN? 2) Are galaxy mergers the dominant AGN triggering mechanism? A complete picture of the AGN-merger connection requires that both of these questions are addressed with the same dataset. In previous work, we have shown that galaxy mergers selected from the Sloan Digital Sky Survey (SDSS) show an excess of both optically-selected, and mid-IR colour-selected AGN…
During galaxy mergers, gas and dust is driven towards the centers of merging galaxies, triggering enhanced star formation and supermassive black hole (SMBH) growth. Theory predicts that this heightened activity peaks at SMBH separations $<$20 kpc; if sufficient material accretes onto one or both of the SMBHs for them to become observable as active galactic nuclei (AGNs) during this phase, they are known as offset and dual AGNs, respectively. To better study these systems, we have built the ACS-AGN Merger Catalog, a large catalog ($N=220$) of uniformly selected offset and dual AGN observed by $…
The occurrence of dual active galactic nuclei (AGN) on scales of a few tens of kpc can be used to study merger-induced accretion on massive black holes (MBHs) and to derive clues on MBH mergers, using dual AGN as a parent population of precursors. We investigate the properties of dual AGN in the cosmological simulation Horizon-AGN. We create catalogs of dual AGN selected with distance and luminosity criteria, plus sub-catalogs where further mass cuts are applied. We divide the sample into dual AGN hosted in different galaxies, on the way to a merger, and into those hosted in one galaxy, after …
We use a phenomenological model which connects the galaxy and AGN populations to investigate the process of AGN triggering through major galaxy mergers at z~0. The model uses stellar mass functions as input and allows the prediction of AGN luminosity functions based on assumed Eddington ratio distribution functions (ERDFs). We show that the number of AGN hosted by merger galaxies relative to the total number of AGN increases as a function of AGN luminosity. This is due to more massive galaxies being more likely to undergo a merger and does not require the assumption that mergers lead to higher…
A direct consequence of hierarchical galaxy formation is the existence of dual supermassive black holes (SMBHs), which may be preferentially triggered as active galactic nuclei (AGN) during galaxy mergers. Despite decades of searching, however, dual AGNs are extremely rare, and most have been discovered serendipitously. Using the all-sky WISE survey, we identified a population of over 100 morphologically identified interacting galaxies or mergers that display red mid-infrared colors often associated in extragalactic sources with powerful AGNs. The vast majority of these advanced mergers are op…
Using numerical hydrodynamics code, we perform various idealized galaxy merger simulations to study the star formation (SF) of two merging disk galaxies. Our simulations include gas accretion onto supermassive black holes and active galactic nucleus (AGN) feedback. By comparing AGN simulations with those without AGNs, we attempt to understand when the AGN feedback effect is significant. With ~70 simulations, we investigated the SF with the AGN effect in mergers with variety of mass ratios, inclinations, orbits, galaxy structures and morphologies. Using these merger simulations with AGN feedbac…
Galaxy mergers are predicted to trigger accretion onto the central supermassive black holes, with the highest rates occurring during final coalescence. Previously, we have shown elevated rates of both optical and mid-IR selected active galactic nuclei (AGN) in post-mergers, but to date the prevalence of X-ray AGN has not been examined in the same systematic way. We present XMM-Newton data of 43 post-merger galaxies selected from the Sloan Digital Sky Survey along with 430 non-interacting control galaxies matched in stellar mass, redshift, and environment in order to test for an excess of hard …
The kinematic disturbances associated with major galaxy mergers are known to produce gas inflows, which in turn may trigger accretion onto the supermassive black holes (SMBH) of the participant galaxies. While this effect has been studied in galaxy pairs, the frequency of active galactic nuclei (AGN) in fully coalesced post-merger systems is poorly constrained due to the limited size or impurity of extant post-merger samples. Previously, we combined convolutional neural network (CNN) predictions with visual classifications to identify a highly pure sample of 699 post-mergers in deep r-band ima…
Active galactic nuclei (AGN), particularly the most luminous AGN, are commonly assumed to be triggered through major mergers, however observational evidence for this scenario is mixed. To investigate any influence of galaxy mergers on AGN triggering and luminosities through cosmic time, we present a sample of 106 luminous X-ray selected type 1 AGN from the COSMOS survey. These AGN occupy a large redshift range (0.5 < z < 2.2) and two orders of magnitude in X-ray luminosity ($\sim$10$^{43}$ - 10$^{45}$ erg s$^{-1}$). AGN hosts are carefully mass and redshift matched to 486 control galaxies. A n…
We present a study of the incidence of active galactic nucleus (AGN) in a sample of major merging systems at 0.3<z<2.5. Galaxies in this merger sample have projected separations between 3 to 15 kpc and are selected from the CANDELS/3D-HST catalogs using a peak-finding algorithm. AGNs in mergers and non-mergers are identified on the basis of their X-ray emission, optical lines, mid-infrared colors, and radio emission. Among galaxies with adequate measurements to find potential AGNs, we find a similar fraction of AGNs in mergers (16.4%) compared to the fraction found in non-merging galaxies (15.…
Galaxy mergers are likely to play a role in triggering active galactic nuclei (AGN), but the conditions under which this process occurs are poorly understood. In Paper I, we constructed a sample of spatially offset X-ray AGN that represent galaxy mergers hosting a single AGN. In this paper, we use our offset AGN sample to constrain the parameters that affect AGN observability in galaxy mergers. We also construct dual AGN samples with similar selection properties for comparison. We find that the offset AGN fraction shows no evidence for a dependence on AGN luminosity, while the dual AGN fractio…
We present a multi-wavelength study of the active nucleus and the off-nuclear X-ray sources in the nearby spiral galaxy, NGC 1365 using three simultaneous UV/X-ray observations by AstroSat over a two months period and archival IR observations performed with Spitzer and Herschel. Utilising the data from the Soft X-ray Telescope (SXT) on-board AstroSat, we find spectral variability mainly caused by the variation in the X-ray column density, (N$_H$ $\sim$ 10$^{22}$ - 10$^{23}$ cm$^{-2}$). With the accurate spatial resolution of the UVIT onboard AstroSat, we separate the intrinsic AGN flux from th…
Galaxy interactions are thought to be one of the main triggers of Active Galactic Nuclei (AGN), especially at high luminosities, where the accreted gas mass during the AGN lifetime is substantial. Evidence for a connection between mergers and AGN, however, remains mixed. Possible triggering mechanisms remain particularly poorly understood for luminous AGN, which are thought to require triggering by major mergers, rather than secular processes. We analyse the host galaxies of a sample of 20 optically and X-ray selected luminous AGN (log($L_{bol}$ [erg/s]) $>$ 45) at z $\sim$ 0.6 using HST WFC3 …
We use the Wide-field Infrared Survey Explorer (WISE) and the Sloan Digital Sky Survey (SDSS) to confirm a connection between dust-obscured active galactic nuclei (AGNs) and galaxy merging. Using a new, volume-limited (z <= 0.08) catalog of visually-selected major mergers and galaxy-galaxy interactions from the SDSS, with stellar masses above 2x10^10 Msun, we find that major mergers (interactions) are 5-17 (3-5) times more likely to have red [3.4]-[4.6] colors associated with dust-obscured or `dusty' AGNs, compared to non-merging galaxies with similar masses. Using published fiber spectral dia…
We investigate the role of galaxy mergers in triggering 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_sun > 10.5 and 0.02 < z < 0.06. We find 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 non-inte…
The major merger-active galactic nucleus connection up to the cosmic noon
SRON Netherlands Institute for Space Research（荷兰空间研究所）；Kapteyn Astronomical Institute, University of Groningen（格罗宁根大学卡普坦天文研究所）；European Space Agency/ESTEC（欧洲航天局/欧洲空间研究与技术中心）；Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México（墨西哥国立自治大学无线电天文学与天体物理研究所）；School of Physics and Astronomy, University of Nottingham（诺丁汉大学物理与天文学院）
We investigate the old open cluster M67 using ultraviolet photometric data of Ultra-Violet Imaging Telescope in multi-filter far-UV bands. M67, well known for the presence of several blue straggler stars (BSS), has been put to detailed tests to understand their formation pathways. Currently, there are three accepted formation channels: mass transfer due to Roche-lobe overflow in binary systems, stellar mergers either due to dynamical collisions or through coalescence of close binaries. So far, there had not been any confirmed detection of a white dwarf (WD) companion to any of the BSSs in this…
The relationship between active galactic nuclei activity and environment has been long discussed, but it is unclear if these relations extend into the dwarf galaxy mass regime -- in part due to the limits in both observations and simulations. We aim to investigate if the merger histories and environments are significantly different between AGN and non-AGN dwarf galaxies in cosmological simulations, which may be indicative of the importance of these for AGN activity in dwarf galaxies, and whether these results are in line with observations. Using the IllustrisTNG flagship TNG100-1 run, 6\,771 d…
Tracing the AGN-Merger Connection: insights from cosmological simulations and JWST mock observations
University of Seoul（首尔大学）；Flatiron Institute（平顿研究所）；Colby College（科尔比学院）；École Polytechnique Fédérale de Lausanne (EPFL)（洛桑联邦理工学院）；University of Copenhagen（哥本哈根大学）；Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理学研究所）；University of Florida（佛罗里达大学）；Space Telescope Science Institute（太空望远镜科学研究所）；Korea Institute for Advanced Study (KIAS)（韩国高等科学研究院）
The co-evolution of galaxies and the supermassive black holes (SMBHs) at their centers via hierarchical galaxy mergers is a key prediction of $Λ$CDM cosmology. As gas and dust are funneled to the SMBHs during the merger, the SMBHs light up as active galactic nuclei (AGNs). In some cases, a merger of two galaxies can encounter a third galaxy, leading to a triple merger, which would manifest as a triple AGN if all three SMBHs are simultaneously accreting. Using high-spatial resolution X-ray, near-IR, and optical spectroscopic diagnostics, we report here a compelling case of an AGN triplet with m…
We investigate the connection between galaxy--galaxy mergers and enhanced black hole (BH) growth using the cosmological hydrodynamical EAGLE simulation. We do this via three methods of analysis, investigating: the merger fraction of AGN, the AGN fraction of merging systems and the AGN fraction of galaxies with close companions. In each case, we find an increased abundance of AGN within merging systems relative to control samples of inactive or isolated galaxies (by up to a factor of $\approx 3$ depending on the analysis method used), confirming that mergers are enhancing BH accretion rates for…
Hierarchical models of galaxy formation predict that galaxy mergers represent a significant transitional stage of rapid supermassive black hole (SMBH) growth. Yet, the connection between the merging process and enhanced active galactic nuclei (AGN) activity as well as the timescale of SMBH mergers remains highly uncertain. The breakthrough in reconciling the importance of galaxy mergers with black hole growth lies in a thoroughly-studied census of dual AGN across cosmic history, which will be enabled by next-generation observational capabilities, theoretical advances, and simulations. This whi…
Offset active galactic nuclei (AGNs) are AGNs that are in ongoing galaxy mergers, which produce kinematic offsets in the AGNs relative to their host galaxies. Offset AGNs are also close relatives of dual AGNs. We conduct a systematic search for offset AGNs in the Sloan Digital Sky Survey, by selecting AGN emission lines that exhibit statistically significant line-of-sight velocity offsets relative to systemic. From a parent sample of 18314 Type 2 AGNs at z<0.21, we identify 351 offset AGN candidates with velocity offsets of 50 km/s < |v| < 410 km/s. When we account for projection effects in th…
Observational studies are increasingly finding evidence against major mergers being the dominant mechanism responsible for triggering AGN. After studying the connection between major mergers and AGN with the highest Eddington ratios at z=2, we here expand our analysis to z<0.2, exploring the same AGN parameter space. Using ESO VLT/FORS2 B-, V- and color images, we examine the morphologies of 17 galaxies hosting AGNs with Eddington ratios >0.3, and 25 mass- and redshift-matched control galaxies. To match the appearance of the two samples, we add synthetic point sources to the inactive compariso…
Double-peaked narrow emission lines in active galactic nucleus (AGN) spectra can be produced by AGN outflows, rotation, or dual AGNs, which are AGN pairs in ongoing galaxy mergers. Consequently, double-peaked narrow AGN emission lines are useful tracers of the coevolution of galaxies and their supermassive black holes, as driven by AGN feedback and AGN fueling. We investigate this concept further with follow-up optical longslit observations of a sample of 95 Sloan Digital Sky Survey (SDSS) galaxies that have double-peaked narrow AGN emission lines. Based on a kinematic analysis of the longslit…
We examine the host morphologies of heavily obscured active galactic nuclei (AGN) at $z\sim1$ to test whether obscured supermassive black hole growth at this epoch is preferentially linked to galaxy mergers. Our sample consists of 154 obscured AGN with $N_{\rm H}>10^{23.5}$ cm$^{-2}$ and $z<1.5$. Using visual classifications, we compare the morphologies of these AGN to control samples of moderately obscured ($10^{22}$ cm$^{-2}$ $<N_{\rm H}< 10^{23.5}$ cm$^{-2}$) and unobscured ($N_{\rm H}<10^{22}$ cm$^{-2}$) AGN. These control AGN are matched in redshift and intrinsic X-ray luminosity to our h…
We examine whether galaxy environments directly affect triggering nuclear activity in Sloan Digital Sky Survey (SDSS) local spiral galaxies using a volume-limited sample with the $r$-band absolute magnitude $M_{r} < -19.0$ and $0.02 < z < 0.055$ selected from the SDSS Data Release 7. To avoid incompleteness of the central velocity dispersion $σ$ of the volume-limited sample and to fix the black hole mass affecting AGN activity, we limit the sample to a narrow $σ$ range of $130$ km s$^{-1}<σ<200$ km s$^{-1}$. We define a variety of environments as a combination of neighbour interactions and loc…
While major mergers have long been proposed as a driver of both AGN activity and the M-sigma relation, studies of moderate to high redshift Seyfert-luminosity AGN hosts have found little evidence for enhanced rates of interactions. However, both theory and observation suggest that while these AGN may be fueled by stochastic accretion and secular processes, high-luminosity, high-redshift, and heavily obscured AGN are the AGN most likely to be merger-driven. To better sample this population of AGN, we turn to infrared selection in the CANDELS/COSMOS field. Compared to their lower-luminosity and …
Recent observations and simulations have challenged the long-held paradigm that mergers are the dominant mechanism driving the growth of both galaxies and supermassive black holes (SMBH), in favour of non-merger (secular) processes. In this pilot study of merger-free SMBH and galaxy growth, we use Keck Cosmic Web Imager spectral observations to examine four low-redshift ($0.043 < z < 0.073$) disk-dominated `bulgeless' galaxies hosting luminous AGN, assumed to be merger-free. We detect blueshifted broadened [OIII] emission from outflows in all four sources, which the \oiii/\hbeta~ratios reveal …
We use zoom simulations to show how merger-driven disruption of the gas disc in a galaxy provides its central active galactic nucleus (AGN) with fuel to drive outflows that entrain and expel a significant fraction of the circumgalactic medium (CGM). This in turn suppresses replenishment of the interstellar medium, causing the galaxy to quench up to several Gyr after the merger. We start by performing a zoom simulation of a present-day star-forming disc galaxy with the EAGLE galaxy formation model. Then, we re-simulate the galaxy with controlled changes to its initial conditions, using the gene…
Among the many processes involved in galaxy evolution, those of bar formation, quenching, and feedback from an active galactic nucleus (AGN) seem to be connected, however, the nature of these relations remains unclear. In this work, we aim to elucidate them by studying the formation of a barred galaxy in a major merger of two disks in the IllustrisTNG simulations. This merger involves a coalescence of two supermassive black holes and a sudden switch to the kinetic mode of AGN feedback implemented in the simulations, which leads to the removal of the gas from the inner part of the galaxy, follo…
Galaxy pairs with separations of only a few kpc represent important stages in the merger-driven growth of supermassive black holes (SMBHs). However, such mergers are difficult to identify observationally due to the correspondingly small angular scales. In Paper I we presented a method of finding candidate kpc-scale galaxy mergers that is leveraged on the selection of X-ray sources spatially offset from the centers of host galaxies. In this paper we analyze new Hubble Space Telescope (HST) WFC3 imaging for six of these sources to search for signatures of galaxy mergers. The HST imaging reveals …
Only obscured yet luminous active galactic nuclei are closely associated with galaxy mergers: Direct observational evidence from type 2 active galactic nuclei
Kyungpook National University（庆北国立大学）；Sejong University（世宗大学）；Pusan National University（釜山国立大学）；Korea Astronomy and Space Science Institute (KASI)（韩国天体宇宙科学研究所）
