X-Ray View of Little Red Dots: Do They Host Supermassive Black
Holes?

ANANNA, Tonima Tasnim, Akos BOGDAN, Orsolya Eszter KOVÁCS, Priyamvada NATARAJAN and Ryan C. HICKOX. X-Ray View of Little Red Dots: Do They Host Supermassive Black Holes? Astrophysical Journal Letters. IOP Publishing Ltd, 2024, vol. 969, No 1, p. 1-10. ISSN 2041-8205. Available from: https://dx.doi.org/10.3847/2041-8213/ad5669.

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TY  - JOUR
ID  - 2418981
AU  - Ananna, Tonima Tasnim - Bogdan, Akos - Kovács, Orsolya Eszter - Natarajan, Priyamvada - Hickox, Ryan C.
PY  - 2024
TI  - X-Ray View of Little Red Dots: Do They Host Supermassive Black Holes?
JF  - Astrophysical Journal Letters
VL  - 969
IS  - 1
SP  - 1-10
EP  - 1-10
PB  - IOP Publishing Ltd
SN  - 20418205
KW  - Active galactic nuclei
KW  - James Webb Space Telescope
KW  - X-ray active galactic nuclei
KW  - Supermassive black holes
UR  - https://iopscience.iop.org/article/10.3847/2041-8213/ad5669
N2  - The discovery of Little Red Dots (LRDs)—a population of compact, high-redshift, dust-reddened galaxies—is one of the most surprising results from JWST. However, the nature of LRDs is still debated: does the near-infrared emission originate from accreting supermassive black holes (SMBHs), or intense star formation? In this work, we utilize ultra-deep Chandra observations and study LRDs residing behind the lensing galaxy cluster, A2744. We probe the X-ray emission from individual galaxies but find that they remain undetected and provide SMBH mass upper limits of ≲(1.5–16) × 106M⊙ assuming Eddington limited accretion. To increase the signal-to-noise ratios, we conduct a stacking analysis of the full sample with a total lensed exposure time of ≈87 Ms. We also bin the galaxies based on their stellar mass, lensing magnification, and detected broad-line Hα emission. For the LRDs exhibiting broad-line Hα emission, there is a hint of a stacked signal (∼2.6σ), corresponding to an SMBH mass of ∼3.2 × 106M⊙. Assuming unobscured, Eddington-limited accretion, this black hole (BH) mass is at least 1.5 orders of magnitude lower than that inferred from virial mass estimates using JWST spectra. Given galaxy-dominated stellar mass estimates, our results imply that LRDs do not host overmassive SMBHs and/or accrete at a few percent of their Eddington limit. However, alternative stellar mass estimates may still support that LRDs host overmassive BHs. The significant discrepancy between the JWST and Chandra data hints that the scaling relations used to infer the SMBH mass from the Hα line and virial relations may not be applicable for high-redshift LRDs.
ER  -

Basic information
Original name	X-Ray View of Little Red Dots: Do They Host Supermassive Black Holes?
Authors	ANANNA, Tonima Tasnim, Akos BOGDAN, Orsolya Eszter KOVÁCS (348 Hungary, belonging to the institution), Priyamvada NATARAJAN and Ryan C. HICKOX.
Edition	Astrophysical Journal Letters, IOP Publishing Ltd, 2024, 2041-8205.

Other information
Original language	English
Type of outcome	Article in a journal
Field of Study	10308 Astronomy
Country of publisher	United Kingdom of Great Britain and Northern Ireland
Confidentiality degree	is not subject to a state or trade secret
WWW	URL
Impact factor	Impact factor: 7.900 in 2022
Organization unit	Faculty of Science
Doi	http://dx.doi.org/10.3847/2041-8213/ad5669
UT WoS	001260083600001
Keywords in English	Active galactic nuclei; James Webb Space Telescope; X-ray active galactic nuclei; Supermassive black holes
Tags	rivok
Tags	International impact, Reviewed
Changed by	Changed by: Mgr. Marie Šípková, DiS., učo 437722. Changed: 18/7/2024 09:43.

Abstract

The discovery of Little Red Dots (LRDs)—a population of compact, high-redshift, dust-reddened galaxies—is one of the most surprising results from JWST. However, the nature of LRDs is still debated: does the near-infrared emission originate from accreting supermassive black holes (SMBHs), or intense star formation? In this work, we utilize ultra-deep Chandra observations and study LRDs residing behind the lensing galaxy cluster, A2744. We probe the X-ray emission from individual galaxies but find that they remain undetected and provide SMBH mass upper limits of ≲(1.5–16) × 106M⊙ assuming Eddington limited accretion. To increase the signal-to-noise ratios, we conduct a stacking analysis of the full sample with a total lensed exposure time of ≈87 Ms. We also bin the galaxies based on their stellar mass, lensing magnification, and detected broad-line Hα emission. For the LRDs exhibiting broad-line Hα emission, there is a hint of a stacked signal (∼2.6σ), corresponding to an SMBH mass of ∼3.2 × 106M⊙. Assuming unobscured, Eddington-limited accretion, this black hole (BH) mass is at least 1.5 orders of magnitude lower than that inferred from virial mass estimates using JWST spectra. Given galaxy-dominated stellar mass estimates, our results imply that LRDs do not host overmassive SMBHs and/or accrete at a few percent of their Eddington limit. However, alternative stellar mass estimates may still support that LRDs host overmassive BHs. The significant discrepancy between the JWST and Chandra data hints that the scaling relations used to infer the SMBH mass from the Hα line and virial relations may not be applicable for high-redshift LRDs.

Links
GX21-13491X, research and development project	Name: Zkoumání žhavého vesmíru a porozumění kosmické zpětné vazbě (Acronym: EHU)
GX21-13491X, research and development project	Investor: Czech Science Foundation

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X-Ray View of Little Red Dots: Do They Host Supermassive Black Holes?

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