J/A+A/682/A36 Massive black holes in nuclear star clusters (Hoyer+, 2024)
Massive black holes in nuclear star clusters.
An investigation with eROSITA/SRG X-ray data.
Hoyer N., Arcodia R., Bonoli S., Merloni A., Neumayer N., Zhang Y.,
Comparat J.
<Astron. Astrophys. 682, A36 (2024)>
=2024A&A...682A..36H 2024A&A...682A..36H (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies ; X-ray sources ; Associations, stellar
Keywords: galaxies: nuclei - galaxies: star clusters: general - X-rays: galaxies
Abstract:
Massive black holes (MBHs) are typically hosted in the centres of
massive galaxies but they appear to become rarer in lower mass
galaxies, where nuclear star clusters (NSCs) frequently appear
instead. The transition region, where both an MBH and NSC can
co-exist, has been poorly studied to date and only a few dozen
galaxies are known to host them. One avenue for detecting new galaxies
with both an MBH and NSC is to look for accretion signatures of MBHs.
Here, we use new SRG/eROSITA all-sky survey eRASS:4 data to search for
X-ray signatures of accreting MBHs in NSCs, while also investigating
their combined occupation fraction.
We collected more than 200 galaxies containing an NSC, spanning
multiple orders in terms of galaxy stellar mass and morphological
type, within the footprint of the German eROSITA Consortium survey. We
determined the expected X-ray contamination from binary stellar
systems using the galaxy stellar mass and star formation rate as
estimated from far-ultraviolet and mid-infrared emission.
We find significant detections for 18 galaxies (∼8.3%), including one
ultra-luminous X-ray source; however, only three galaxies (NGC 2903,
4212, and 4639) have X-ray luminosities that are higher than the
expected value from X-ray binaries, indicative of the presence of an
MBH. In addition, the X-ray luminosity of six galaxies (NGC 2903,
3384, 4321, 4365, 4639, and 4701) differs from previous studies and
could indicate the presence of a variable active galactic nucleus. For
NGC 4701 specifically, we find a variation of X-ray flux within the
eRASS:4 data set. Stacking X-ray non-detected galaxies in the dwarf
regime M*gal≤109M☉) results in luminosity upper limits of a
few times 1038erg/s. The combined occupation fraction of
accreting MBHs and NSCs becomes non-zero for galaxy masses above
∼107.5M☉ and this result is slightly elevated as compared to
the literature data.
Our data extend, for the first time, towards the dwarf elliptical
galaxy regime and identify promising MBH candidates for higher
resolution follow-up observations. At most galaxy masses (and with the
exception of three cases), the X-ray constraints are consistent with
the expected emission from binary systems or an Eddington fraction of
at most 0.01%, assuming a black holes mass of 106.5M☉. This
work confirms the known complexities in similar-type of studies, while
providing the appealing alternative of using X-ray survey data of
in-depth observations of individual targets with higher resolution
instruments.
Description:
We present the basic galaxy properties and X-ray luminosities in the
2-10keV range from eRASS:4, a cumulative data set of four all-sky
surveys of eROSITA onboard SRG. All galaxies listed are known to host
nuclear star clusters.
Contains galaxy names, angular coordinates, distance, morphological
type, and mass estimates, X-ray luminosities in the 2-10keV range, the
cumulative exposure time, and binomial probability that the source is
a background fluctuation.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 195 239 Galaxy properties and X-ray luminosities in the
2-10keV range from eRASS:4
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 27 A27 --- Galaxy Galaxy name (galaxy)
29- 38 F10.6 deg RAdeg Right ascension (J2000) (ra)
40- 48 F9.6 deg DEdeg Declination (J2000) (dec)
50- 55 F6.3 mag distmod ?=- Distance modulus (distmod)
57- 61 F5.3 mag e_distmod ?=- Uncertainty on the distance modulus
(u_distmod)
63- 66 F4.1 --- TType ?=- Morphological Hubble type (ttype)
68- 70 F3.1 --- e_TType ?=- Uncertainty on the morphological
Hubble type (u_ttype)
72- 77 F6.3 [Msun] loggalmass ?=- Logarithmic galaxy stellar mass
(galmass)
79- 83 F5.3 [Msun] e_loggalmass ?=- Uncertainty on the logarithmic
galaxy stellar mass (u_galmass)
85- 96 E12.6 [Msun/yr] logSFR ?=- Logarithmic star formation rate
(logsfr)
98-109 E12.6 [Msun/yr] e_logSFR ?=- Uncertainty on the logarithmic star
formation rate (u_logsfr)
111-122 E12.6 10-7W LumMed2-10 ?=- Median luminosity in the 2-10keV
band (lummedian2to10)
124-135 E12.6 10-7W Lum1st2-10 ?=- 1st percentile of the luminosity in
the 2-10keV band (lum1st2to10)
137-148 E12.6 10-7W Lum99th2-10 ?=- 99th percentile of the luminosity in
the 2-10keV band (lum99th2to10)
150-161 E12.6 10-7W Lumbin ?=- Expected luminosity from binary
systems (lum_binary)
163-174 E12.6 10-7W e_Lumbin ?=- Uncertainty on the expected
luminosity from binary systems
(ulumbinary)
176-182 F7.3 s TExp ?=- eRASS:4 total exposure time (t_exp)
184-195 E12.6 --- pbinom [0/1] Binomial probability that the
detection is a background fluctuation
(p_binom)
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Acknowledgements:
Nils Hoyer, nils.hoyer(at)dipc.org
(End) Patricia Vannier [CDS] 04-Dec-2023