arXiv subjects

Vicki Sarajedini

Publications and source records attributed to Vicki Sarajedini.

9 recordsLinked to original sources

arXiv2026

Constraining Supermassive Black Hole Seeding and Accretion via Occupation Fractions and Mass-Weighted Distributions

The formation of supermassive black holes (SMBHs) is a key open problem in galaxy evolution, with light- and heavy-seeding models predicting distinct black hole occupation fractions (BHOFs). Using multiwavelength observations from the LSST Deep Drilling Fields, we measure the AGN fraction and estimate the BHOF across $0<z<1$. Applying a hierarchical Bayesian model, we find that the inferred BHOF remains $100\%$ for host galaxy masses below $10^9 M_\odot$ at lower redshifts. These findings are consistent with light-seed scenarios. Additionally, we computed the black hole masses for several galaxies in the W-CDF-S to test the mass-weighted black hole occupation distributions from semi-analytic models (SAM). Using a reduced-$χ^2$ analysis, we find that the data are consistent with the main-sequence accretion model regardless of the assumed seeding mechanism. These results provide new observational constraints on SMBH seeding and highlight the value of combining deep extragalactic surveys with probabilistic modeling.

astro-ph.GA↗

arXiv2026

A Quest for Changing-State AGNs

We use Gaia Data Release 3 (DR3) light curves to identify photometrically selected changing-state active galactic nucleus (CSAGN) candidates. We employ unsupervised deep learning and anomaly detection methods to identify unusual patterns of variability in the light curves of 872,228 AGNs with known variability. We find that 8,504 light curves show anomalous behavior. Among these, 682 sources show evidence for two-state photometric behavior during the Gaia DR3 observing baseline. These 682 CSAGN candidates were selected using an automated statistical pattern recognition approach based on Gaussian mixture models (GMMs) to identify sources whose magnitude distributions are consistent with two preferred brightness levels, substantially reducing the need for human visual inspection in selecting the CSAGN candidates. The candidates tend to have fainter absolute magnitudes and lower redshifts than the non-anomalous Gaia variable AGN sample, suggesting that some may be accreting at lower rates. Our approach builds a large candidate sample with less reliance on human visual selection. Follow-up observations of these sources can help identify what drives changing-state transitions and clarify their connection to accretion-disk physics and supermassive black hole (SMBH) fueling.

astro-ph.GA↗

arXiv2024

Ensemble Variability Properties of Active Galactic Nuclei in the SDSS DR17

We present the results from a study of ~9,600 Broad-Line selected AGN with host galaxies detected from the Sloan Digital Sky Survey Data Release 17 (SDSS DR17). We compute ensemble variability statistics based on the comparison of the original SDSS photometric data with spectrophotometric measurements obtained days to decades later in the Sloan g-, r-, and i-bands. Galaxy and AGN templates have been fitted to the SDSS spectra to isolate the AGN component from the host galaxy. The sources have absolute magnitudes in the range -24<M_i<-18 and lie at redshifts less than z~0.9. A variability analysis reveals that the anti-correlation between luminosity and variability amplitude continues down to log(L_bol[erg/s]) = 43.5, demonstrating that the relationship extends by 4 orders of magnitude in AGN luminosity. To further explore the connection between AGN luminosity and variability, we determine the black hole mass and the accretion rate through measurement of the H-Beta line width and the monochromatic luminosity at rest-frame 5,100 angstrom. Our results suggest that the accretion rate is the dominant parameter impacting the amplitude of variability and that the anti-correlation between accretion rate and amplitude extends to rates as low as 1% Eddington. Moreover, we also identify an anti-correlation between variability amplitude and black hole mass, with the correlation appearing strongest among the AGN with low accretion rates.

astro-ph.GA↗

arXiv2012

The SEDs, Host Galaxies and Environments of Variability Selected AGN in GOODS-S

Variability selection has been proposed as a powerful tool for identifying both low-luminosity AGN and those with unusual SEDs. However, a systematic study of sources selected in such a way has been lacking. In this paper, we present the multi-wavelength properties of the variability selected AGN in GOODS South. We demonstrate that variability selection indeed reliably identifies AGN, predominantly of low luminosity. We find contamination from stars as well as a very small sample of sources that show no sign of AGN activity, their number is consistent with the expected false positive rate. We also study the host galaxies and environments of the AGN in the sample. Disturbed host morphologies are relatively common. The host galaxies span a wide range in the level of ongoing star-formation. However, massive star-bursts are only present in the hosts of the most luminous AGN in the sample. There is no clear environmental preference for the AGN sample in general but we find that the most luminous AGN on average avoid dense regions while some low-luminosity AGN hosted by late-type galaxies are found near the centres of groups. AGN in our sample have closer nearest neighbours than the general galaxy population. We find no indications that major mergers are a dominant triggering process for the moderate to low luminosity AGN in this sample. The environments and host galaxy properties instead suggest secular processes, in particular tidal processes at first passage and minor mergers, as likely triggers for the objects studied. This study demonstrates the strength of variability selection for AGN and gives first hints at possibly triggering mechanisms for high-redshift low luminosity AGN.

astro-ph.CO↗

arXiv2007

Optical Variability of Infrared Power Law-Selected Galaxies & X-ray Sources in the GOODS-South Field

We investigate the use of optical variability to identify and study Active Galactic Nuclei (AGN) in the GOODS-South field. A sample of 22 mid-infrared power law sources and 102 X-ray sources with optical counterparts in the HST ACS images were selected. Each object is classified with a variability significance value related to the standard deviation of its magnitude in five epochs separated by 45-day intervals. The variability significance is compared to the optical, mid-IR, and X-ray properties of the sources. We find that 26% of all AGN candidates (either X-ray- or mid-IR-selected) are optical variables. The fraction of optical variables increases to 51% when considering sources with soft X-ray band ratios. For the mid-IR AGN candidates which have multiwavelength SEDs, we find optical variability for 64% of those classified with SEDs like Broad Line AGNs. While mostly unobscured AGN appear to have the most significant optical variability, some of the more obscured AGNs are also observed as variables. In particular, we find two mid-IR power law-selected AGN candidates without X-ray emission that display optical variability, confirming their AGN nature.

astro-ph↗

arXiv2005

The DEEP Groth Strip Survey. I. The Sample

The Deep Extragalactic Exploratory Probe (DEEP) is a multi-phase research program dedicated to the study of the formation and evolution of galaxies and of large scale structure in the distant Universe. This paper describes the first five-year phase, denoted DEEP1. A series of ten DEEP1 papers will discuss a range of scientific topics (e.g., the study of photometric and spectral properties of a general distant galaxy survey, the evolution observed in galaxy populations of varied morphologies). The observational basis for these studies is the Groth Survey Strip field, a 127 square arcminute region which has been observed with the Hubble Space Telescope in both broad I-band and V-band optical filters and with the Low Resolution Imaging Spectrograph on the Keck Telescopes. Catalogs of photometric and structural parameters have been constructed for 11,547 galaxies and stars at magnitudes brighter than 29, and spectroscopy has been conducted for a magnitude-color weighted subsample of 818 objects. We evaluate three independent techniques for constructing an imaging catalog for the field from the HST data, and discuss the depth and sampling of the resultant catalogs. The selection of the spectroscopic subsample is discussed, and we describe the multifaceted approach taken to prioritizing objects of interest for a variety of scientific subprograms. A series of Monte Carlo simulations then demonstrates that the spectroscopic subsample can be adequately modeled as a simple function of magnitude and color cuts in the imaging catalog.

astro-ph↗

arXiv2004

Multiwavelength Properties of the X-ray Sources in the Groth-Westphal Strip Field

We summarize the multiwavelength properties of X-ray sources detected in the 80 ks XMM-Newton observation of the Groth-Westphal Strip. We find 23 XMM-Newton sources within the WFPC2 fields. Ten spectroscopic redshifts are available from the DEEP and CFRS projects and 4 of these show broad Mg II emission (type 1 AGNs). Two of those without any broad lines, nevertheless, have [NeV] emission which is an unambiguous signature of AGN activity, one of which is a narrow-line Seyfert 1 and the other a type 2 AGN. We have made near-infrared (NIR) spectroscopic observations using the Subaru OHS/CISCO spectrometer for five of the X-ray sources for which we found no indication of an AGN activity in the optical spectrum. We have detected H-alpha+[NII] emission in four of them. A broad H-alpha component and/or a large [NII]/H-alpha ratio is seen, suggestive of AGN activity. Nineteen sources have been detected in the Ks band and four of these are extremely red objects (I814-Ks>4). The optical counterparts for the majority of the X-ray sources are bulge-dominated with colors consistent with evolving elliptical galaxies, with starburst/AGN contamination. Assuming that the known local relations among the bulge luminosity,central velocity dispersion, and the mass of the central blackhole hold at about z=1, the AGN bolometric luminosity to Eddington luminosity ratio ranges from 0.3% to 10%. (abridged)

astro-ph↗

arXiv2001

Objective-Prism Emission-Line Searches for Active Galactic Nuclei

Objective-prism surveys for UV-excess and emission-line objects, especially the First and Second Byurakan Surveys, have been central to the study of active galactic nuclei (AGNs). We review previous line-selected surveys for AGNs and discuss their contribution to our understanding of the AGN phenomena. In addition, we present results from the KPNO International Spectroscopic Survey, a modern digital objective-prism survey for emission line objects. This survey is discovering substantial numbers of new AGNs, in particular low-luminosity AGNs and LINERs.

astro-ph↗

arXiv2001

Spectroscopic and Variability Surveys for AGN in the Groth Survey Strip

Preliminary results are presented for a spectroscopic survey of the Groth Survey Strip (GSS), a 40 by 3.5 arcminute region of the sky imaged with HST, for which several hundred galaxy spectra have been obtained as part of the DEEP project (http://deep.ucolick.org). At least 6 broad-line AGNs (primarily Seyfert 1s) have been detected as well as several narrow-line Seyfert 2 candidates. The Seyfert galaxies detected in our survey have integrated absolute magnitudes extending to M(B)~-17.5, probing fainter magnitudes and higher redshifts than existing optical spectroscopic surveys. We also discuss a variability study of the GSS using the original HST images from 1994 and new images obtained in 2001. The high resolution obtained with HST allows us to isolate and measure variable galactic nuclei too faint to be detected from the ground, reaching nuclear magnitudes of M(B)~-16 in galaxies to z=0.8. The combination of these techniques provides a powerful probe of the population of low-luminosity AGNs at moderate redshifts.

astro-ph↗