Nico Cappelluti ,1,2 3 4,5,6 arXiv:2109.08701v2 [astro-ph ...

1 Draft version December 22, 2021 Typeset using LATEX twocolumnstyle in AASTeX63 Exploring the high-redshift PBH- CDM Universe: early black hole seeding, the first stars and cosmicradiation Cappelluti ,1, 2G unther Hasinger,3and Priyamvada Natarajan4, 5, 61 Department of Physics, University of Miami, Coral Gables, FL 33124, USA2 INAF Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy3 European Space Astronomy Centre (ESA/ESAC) E-28691 Villanueva de la Ca nada, Madrid, Spain4 Department of Astronomy, Yale University, 52 Hillhouse Avenue, New Haven, CT 06520, USA5 Department of Physics, Yale University, Box 208121, New Haven, CT 06520, USA6 Black Hole Initiative, Harvard University, 20 Garden Street, Cambridge MA 02138, USAS ubmitted to ApJABSTRACTWe explore the observational implications of a model in which primordial black holes (PBHs)

2 With abroad birth mass function ranging in mass from a fraction of a solar mass to 106M , consistent withcurrent observational limits, constitute the dark matter component in the Universe. The formationand evolution of dark matter and baryonic matter in this PBH- CDM Universe are presented. Inthis picture, PBH DM mini-halos collapse earlier than in standard CDM, baryons cool to form starsatz 15 20, and growing PBHs at these early epochs start to accrete through Bondi volume emissivity of these sources peaks atz 20 and rapidly fades at lower redshifts. Asa consequence, PBH DM could also provide a channel to make early black hole seeds and naturallyaccount for the origin of an underlying dark matter halo - host galaxy and central black hole connectionthat manifests as theMbh correlation.

3 To estimate the luminosity function and contributionto integrated emission power spectrum from these high-redshift PBH DM halos, we develop a HaloOccupation Distribution (HOD) model. In addition to tracing the star formation and reionizatonhistory, it permits us to evaluate the Cosmic Infrared and X-ray Backgrounds (CIB and CXB). Wefind that accretion onto PBHs/AGN successfully accounts for the detected backgrounds and their cross-correlation, with the inclusion of an additional IR stellar emission component. Detection of the deepIR source count distribution by the JWST could reveal the existence of this population of high-redshiftstar-forming and accreting PBH :editorials, notices miscellaneous catalogs matter (DM) represents the most abundant formof matter in the Universe and dominates the dynam-ics of collapsed objects.

4 It also offers the scaffoldingwithin which all visible matter is structured into galax-ies. Thus far, in the context of the cold dark matterparadigm, it has been widely assumed that DM exists inCorresponding author: Nico form of still unknown particles that interact primar-ily through gravity and perhaps through weak interac-tions ( Feng 2010). However, despite several decadesof targeted experimental searches aimed at uncoveringweakly interacting massive particles as potential darkmatter candidates, these efforts have all come up present there seem to be no sign of particle DM can-didates in the mass interaction cross-section parameterspace and energy ranges where they have been predicted(Baudis 2012; Boveia & Doglioni 2018).Meanwhile, the discovery of gravitational waves frommerging black hole (BH) binaries by LIGO and VIRGO reveal surprisingly large masses for the individual merg- [ ] 21 Dec 20212 Cappelluti , Hasinger & Natarajaning BHs with, on average, low pre-merger spins.

5 Typicalinferred masses of the merging sources are higher thanexpected from astrophysical formation channels (Abbottet al. 2016). Consequently, the community revived thehypothesis originally proposed by Hawking (1971) thatDM could be constituted by Primordial Black Holes(PBHs) that formed in the infant Universe (Jedamzik1997; Carr 2003; Bird et al. 2016; Kashlinsky 2016;Clesse & Garc a-Bellido 2017; Jedamzik 2021).Early models assumed that all dark matter is com-prised of PBHs that formed with a monochromaticmass function, but observational constraints firmly ruleout this hypothesis ( Belotsky et al. 2019). Laterwork and further refinements, notably by Carr et al.(2019), Garc a-Bellido (2019), Carr et al. (2020) andCarr et al. (2021) showed that DM PBHs can, in prin-ciple, have a broad birth mass spectrum ranging from10 10 107M ; while accounting for all the DM with-out violating current observational constraints.

6 In theirmodel, PBHs are created in the early Universe duringQCD phase transitions (around 100 MeV that corre-sponds to 1010K) involving different particle familiesfreezing out of the primordial quark-gluon plasma withinthe first two seconds after the inflationary phase. WhenW+/ , Z bosons, baryons, pions are created, and e+e pairs annihilate, they leave an imprint in form of a signif-icant reduction of the sound speed at the correspondingphase transitions, thereby causing regions of high curva-ture to collapse and form PBHs. The typical mass scaleof these PBHs is defined by the size of the horizon atthe time of the corresponding phase transition. In thismodel, four distinct populations of PBHs in a wide massrange are expected to form: planetary mass black holesat theW+/ -Z transition; PBHs of around the Chan-drasekhar mass when the baryons (protons and neu-trons) form from 3 quarks; PBHs with masses of order30 M (these correspond to the suggested LIGO blackholes), when pions form from two quarks; and finallyPBHs with masses corresponding to those of supermas-sive black holes (SMBHs) withM 106M that format the e+e annihilation.

7 If PBHs form with a broadmass distribution, the DM they constitute is expectedto strongly cluster, which would help alleviate some ofthe more stringent observational constraints on the al-lowed contribution of PBHs to the dark matter (Clesse& Garc a-Bellido 2017; Belotsky et al. 2019) , an excess of small-scale DM substruc-ture compared to CDM predictions has been recentlyreported from gravitational cluster lensing studies withthe deepest HST observations (Meneghetti et al. 2020).Clustering of DM in excess of what is predicted by thestandard WIMP CDM paradigm as expected with PBHDM, could possibly account for this discrepancy. Thisexcess concentration of mass on small scales is revealedin the discrepancy between the observed and predictedevent rates for Galaxy-Galaxy Strong Lensing (GGSL)events.

8 The internal structure of subhalos with masses 1011M are implicated for these GGSL events, and CDM simulations simply do not produce enough sub-halos in this range with the requisite central addition to possibly providing a simple resolutionof the nagging DM problem, PBHs it appears could alsoserve to account for early massive black hole seed forma-tion and address the intriguing origin of the SMBHs withmass of the order 1010M powering detected luminousquasars already in place byz >7 when the Universewas< Gyr old (see Lodato & Natarajan 2006a;Li et al. 2007).Quite a number of other recent observational resultsalso strengthen the conjecture that PBHs could con-tribute to the overall DM budget. The latest GWTC-2catalogue of LIGO-Virgo-KAGRA gravitational mergerevents (Abbott et al. 2021) has widened the observed BHmass distribution considerably.

9 In particular, it includesthe most massive merger detected as yet GW190521(Carr et al. 2019; Clesse & Garcia-Bellido 2021; Abbottet al. 2020a), in which at least one of the two compo-nents is more massive than the upper mass gap expectedfor pair instability supernovae (SN), and thus could sig-nal a PBH origin (Clesse & Garcia-Bellido 2021; DeLuca et al. 2021a). It also includes the event GW190814(Abbott et al. 2020b), in which one of the componentslikely falls into the lower SN mass gap between neu-tron stars and BH, and which has a surprisingly largemass ratio of 1:9, not entirely easily compatible withknown astrophysical production channels (De Luca et ). Wong et al. (2021) analyse the whole GWTC-2 catalogue and conclude that the observed event rateis fully consistent with the assumption that all LIGO-VIRGO detected merging BHs are of primordial origin,contributing a fraction offPBH to overall theDM budget in the mass range 1<MBH<100 M.

10 New results from the 5-year OGLE micro-lensingcampaign (Niikura et al. 2019a) present the discoveryof a sizeable population of long-duration micro-lensingevents, which, together with Gaia parallaxes, point tothe presence of putative PBHs in the mass range 1 10 M (Wyrzykowski & Mandel 2020). Another mass-gap BH candidate was recently discovered in the nearbynearly edge-on ellipsoidal variable binary star V723 Mon(Jayasinghe et al. 2021). OGLE has also detected 6ultrashort-timescale microlensing events, which may, infact, indicate the existence of planetary mass PBHsExploring the PBH- CDM Universe3(Niikura et al. 2019a). The NANOGrav pulsar tim-ing observatory has recently reported interesting up-per limits on the stochastic gravitational wave back-ground in the nano-Hertz band in their data, whichdoes not show statistically significant quadrupolar spa-tial correlations expected for a cosmic gravitational wavebackground (Arzoumanian et al.)