arXiv subjects

Emmanuel Durodola

Publications and source records attributed to Emmanuel Durodola.

5 recordsLinked to original sources

arXiv2026

A Population of Little Red Dot-like Quasars in SDSS

Compact and red sources in the high redshift ($z\sim5$) Universe, known as "Little Red Dots" (LRDs), are among JWST's most intriguing discoveries. These sources have broad Balmer emission lines, weak X-ray emission, and unique spectral energy distributions (SEDs) poorly fit by either stellar or AGN templates. Local LRD-like objects allow for detailed studies of the underlying physical processes with archival multi-wavelength datasets unavailable in the high-$z$ Universe. We show that the SDSS $ugriz$ filters at $z\approx0.4, 0.8$ overlap well with the JWST filters used to select LRDs at $z\sim5$. We use SDSS quasars to define a sample of $\sim1300$ Local Red Dots (LoRDs) which share the same photometric colors of LRDs. A subset of the LoRD sample selected to have V-shaped continua ($N=244$) show prominent higher-order Balmer absorption features and [NeV]$\lambda$3426 emission, both of which would likely be missed in JWST/PRISM observations given the low spectral resolution. A composite SED of the LoRDs differs from a typical quasar SED in the rest-frame UV/optical, but the two agree with each other in the NIR. The LoRD SED matches well with a stack of LRDs and can be modeled either as a reddened AGN combined with a host galaxy, or as a reddened AGN combined with a host galaxy and a cool blackbody. Interestingly, the LoRDs are X-ray detected at a rate comparable to typical quasars. However, the probability that LoRDs and typical quasars would go undetected, if subject to the LRD X-ray upper limits, is $>50\%$.

astro-ph.GA↗

arXiv2026

ID-MAGE II: The Star Forming Satellites of Low-Mass Hosts

We present results from our ongoing campaign to follow up the satellite candidates from the Identifying Dwarfs of MC Analog GalaxiEs (ID-MAGE) survey. Previously, we published a list of 355 unresolved satellite candidates identified around 36~nearby LMC- and SMC-mass hosts (D$=$4$-$10~Mpc). We present the velocities of 83 satellite candidates from new Green Bank Telescope \hi\ observations, optical long-slit spectra, and the Dark Energy Survey Instrument Data Release 1. Based on their velocities, we identify six candidates as probable satellite galaxies ($6.5\times10^5\leq M_\star/M_\odot\leq1.5\times10^7$) and 77 as background galaxies. Our results underscore the ability of spectroscopic follow-up to effectively separate satellites from background galaxies. Using the refined sample, we update our previously derived estimates for the average satellite population per host and find 1.7$\pm$0.7 (1.0$\pm$0.3) satellites per LMC-mass (SMC-mass) host. Our current satellite sample includes 25 galaxies confirmed by distances or velocities. This set includes the complete satellite populations of three hosts (UGC~04422: zero satellites, UGC~08201: zero satellites, NGC~3432: four satellites), which we compare to simulations and known satellite systems from the literature. Our sample is nearly complete for the most massive satellites (M$_\star > 10^7~M_\odot$). We find these massive satellites have a quenched fraction of 10--25\%, placing them between the $<$5\% quenched fraction of isolated galaxies and the 40--70\% quenched fraction of MW-analog satellites with $10^7~M_\odot < $ M$_\star < 10^8~M_\odot$. This demonstrates the impact that low-mass galaxies have on the evolution of their satellites.

astro-ph.GA↗

arXiv2026

Identifying Dwarfs of MC Analog GalaxiEs (ID-MAGE): The Search for Satellites Around Low-Mass Hosts

We present results from ID-MAGE (Identifying Dwarfs of MC Analog GalaxiEs), a survey aimed at identifying and characterizing unresolved satellite galaxies around 36~nearby LMC- and SMC-mass hosts (D$=$4$-$10~Mpc). We use archival DESI Legacy Survey imaging data and perform an extensive search for dwarf satellites, extending out to a radius of 150~kpc ($\sim$$R_{vir}$). We identify 355 candidate satellite galaxies, including 264 new discoveries. Extensive tests with injected galaxies demonstrate that the survey is complete down to $M_V\sim-$9.0 (assuming the distance of the host) and $μ_{0,V}\sim$26 mag arcsec$^{-2}$ (assuming a n$=$1 Sérsic profile). We perform consistent photometry, via Sérsic profile fitting, on all candidates and have initiated a comprehensive follow-up campaign to confirm and characterize candidates. Through a systematic visual inspection campaign, we classify the top candidates as high-likelihood satellites. On average, we find 4.0$\pm$1.4 high-likelihood candidate satellites per LMC-mass host and 2.1$\pm$0.6 per SMC-mass host which is within the range predicted by cosmological models. We use this sample to establish upper and lower estimates on the satellite luminosity function of LMC/SMC-mass galaxies. ID-MAGE nearly triples the number of low-mass galaxies surveyed for satellites with well-characterized completeness limits, providing a unique dataset to explore small-scale structure and dwarf galaxy evolution around low-mass hosts in diverse environments.

astro-ph.GA↗

arXiv2025

Exploring the AGN Fraction of a Sample of JWST's Little Red Dots at $5 < z < 8$: Overmassive Black Holes Are Strongly Favored

JWST is revolutionizing our view of the early Universe by pushing the boundaries of detectable galaxies and black holes in redshift (upward) and mass (downward). The Little Red Dots (LRDs), detected by several surveys at $z > 4$, present a significant interpretational challenge, as their Spectral Energy Distributions (SED) can mimic both AGN and stellar population templates. This study analyzes 19 LRDs from the JADES survey, utilizing NIRCam and MIRI photometry. By performing SED fitting across a vast parameter space, we explore a broad range of AGN fractions, defined as the ratio of the monochromatic luminosities (AGN, galaxy, and dust) over a specified wavelength range, 0.4 - 0.7 $μm$ rest-frame. We find that 17 of the 19 LRDs investigated are consistent with having significant AGN contributions, with best-fitting AGN fractions ranging between 20% and 70%, while one galaxy shows a low AGN contribution (2%) and another appears to be purely star-forming. Moreover, assuming these LRDs do indeed host AGN, we can place limits on their black hole masses using the inferred AGN bolometric luminosities and adopting the Eddington limit. We find that, independent of the specific AGN fraction adopted, the LRDs' black holes are significantly overmassive relative to their host galaxies (by $\sim 1$ dex, and up to $\sim 4$ dex in the most extreme cases) compared to the local $M_{\bullet} - M_{\star}$ relation. The presence of overmassive black holes in the high-$z$ Universe may provide the strongest evidence yet of heavy black hole seeding occurring during the cosmic dark ages.

astro-ph.GA↗

arXiv2025

Evidence for evolutionary pathway-dependent black hole scaling relations

Recent observations have identified an abundance of high-redshift active galactic nuclei (AGN) with supermassive black holes (BHs) that are over-massive compared to the local BH mass$-$total stellar mass ($M_{\mathrm{BH}}-M_\star$) relation. $M_{\mathrm{BH}}$ measurements at high-$z$ are critical for probing the growth histories of BHs and their host galaxies, including BH seeding and evolution of the $M_{\mathrm{BH}}-M_\star$ relation. However, BH masses in high-$z$ AGN are generally estimated from single-epoch measurements, which are anchored to local relations based on reverberation mapping and carry large systematic uncertainties. Alternate $M_{\mathrm{BH}}$ detection methods such as dynamical measurements are more reliable but currently only possible in the local Universe or with strongly lensed systems. Recently, dynamical $M_{\mathrm{BH}}$ measurements were made in a $z\sim2$ lensed quiescent galaxy as well as a sample of six local galaxies identified as likely relics of common quiescent red nugget galaxies at cosmic noon. We compare the $z\sim2$ red nugget and relic BHs to recent results for $4<z<11$ AGN, quasars, and Little Red Dots. Intriguingly, the $z\sim2$ galaxy and local relic galaxies all lie on both the local $M_{\mathrm{BH}}-M_\star$ relation for bulges and the $4<z<7$ $M_{\mathrm{BH}}-M_\star$ relation. Our results suggest the $M_{\mathrm{BH}}-M_\star$ relation for bulges was likely in place at high-$z$ and indicate careful consideration of different evolutionary pathways is needed when building BH scaling relations. While improvements to $M_{\mathrm{BH}}$ estimates in AGN will increase our confidence in high-$z$ BH masses, detecting BHs in relic galaxies and lensed galaxies presents a complementary probe of the high-$z$ relations.

astro-ph.GA↗