DRAFT VERSION J UNE 28, 2024 Typeset using L A T E X twocolumn style in AASTeX63 Chandra detects low-luminosity AGN with M BH = 10 4 − 10 6 M ⊙ in nearby (z< 0.5), dwarf and star-forming galaxies MAINAK SINGHA , 1, 2, 3 J ULISSA SARMIENTO, 4 SANGEETA MALHOTRA , 1 JAMES E. RHOADS, 1 L. Y. AARON YUNG , 5 J UNXIAN WANG, 6 ZHEN-YA ZHENG , 7, 8 RUQIU LIN, 7, 8 KEUNHO KIM , 9 J IALAI KANG, 10 AND SANTOSH HARISH 11 1 Astrophysics Science Division, NASA, Goddard Space Flight Center, Greenbelt, MD 20771, USA 2 Department of Physics, The Catholic University of America, Washington, DC 20064, USA 3 Center for Research and Exploration in Space Science and Technology, NASA, Goddard Space Flight Center, Greenbelt, MD 20771, USA 4 Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260, USA 5 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA 6 CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei 230026, China 7 Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, China 8 School of Astronomy and Space Sciences, University of Chinese Academy of Sciences, Beijing 100049, China 9 IPAC, California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125, USA 10 University of Science and Technology of China, Hefei 230026, People’s Republic of China 11 Laboratory for Multiwavelength Astrophysics, School of Physics and Astronomy, Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, NY 14623, USA ABSTRACT We searched the Chandra and XMM archives for observations of 900 green pea galaxies to seek signatures of AGN. Green peas are low-mass galaxies with prominent emission lines, and have remarkably similar properties (such as size, star formation rate) compared to redshift, z> 7 dwarf galaxies. Out of the 29 observations found in the archives, 9 show detections in X-rays at S/N > 3. The upper limits of others are also pretty similar. The 2-10 keV X-ray luminosity for the 9 sources exceeds 10 40 erg s −1 , and 2 sources show 2-10 keV X-ray luminosity greater than 10 41 erg s −1 , suggesting the presence of intermediate mass black holes (IMBH)/low- luminosity AGN (LLAGN), corresponding to BH mass, M BH = 100 − 10 6 M ⊙ . All of the X-ray detected sources (plus 6 additional sources) show He IIλ4686 emission and a broad component of the Hα emission line indicating the presence of winds. The line widths of the broad Hα and He IIλ4686 emitting gas clouds are only weakly correlated (R 2 =0.15), suggesting that He IIλ4686 emission is inconsistent with winds from super-Eddington accretors. However, the ratio of X-ray luminosity to star-formation rate is consistent with an anti-correlation with metallicity for 5 out of 9 sources with X-ray detection. Such anti-correlation suggests that ultraluminous X-ray sources could be the key contributors to the observed X-ray luminosity, which could be either: (i) super-Eddington accretors, or (ii) intermediate mass black holes (IMBH). The observed X-ray emission is at least an order of magnitude higher than what could be produced by Wolf-Rayet stars and fast radiative shocks from supernovae-driven winds. The X-ray luminosity in all 9 sources could, therefore, only be explained by black holes with masses exceeding 100 M ⊙ . Our results suggest that the X-ray emission in our sources requires a LLAGN. The line widths of broad Hα, if due to accretion onto massive BH, imply masses of M BH = 10 4 − 10 6 M ⊙ . Since Green Peas have been shown to be significant Lyman Continuum leakers, the presence of LLAGN in these galaxies would imply that that such AGN might have significantly contributed to the cosmic reionization. Keywords: galaxies:Galaxy, Lyman-alpha, Star-formation, AGN 1. INTRODUCTION A fundamental unsolved problem in observational cosmol- ogy galaxy formation is the role of accreting supermassive black holes (SMBH) or active galactic nuclei (AGN) in ion- izing the universe during the cosmic reionization. AGN fu- elled by the accreting energy are more efficient in producing hard-ionizing photons—such as He IIλ4686 (Giallongo et al. 2015; Yung et al. 2021). This leads to many studies propose the idea that AGN might have served as a significant source of ionizing photons, compared to starburst-driven processes (Madau & Haardt 2015; Volonteri et al. 2016). Whereas the general consensus is that the AGN number density is insuf- ficiently high at elevated redshifts to accomplish complete reionization. Instead, it is widely believed that galactic ultra- arXiv:2406.18730v1 [astro-ph.GA] 26 Jun 2024