We present new upper limits for black hole masses in extremely late type spiral galaxies. We confirm that this class of galaxies has black holes with masses less than 106
Supermassive black holes (BHs) are thought to be ubiquitous in the nuclei of massive galaxies. The discovery of a number of tight correlations between the global properties of galaxies and the properties of their nuclei (e.g., [
The overall nucleation frequency is around 75% over all Hubble types ([
Intriguingly, NCs in late-type spirals and dwarf ellipticals follow relationships with their host galaxies that mirror the
A further reason for interest in NCs and their BHs is that a number of authors [
Of the many global-to-nucleus relations, the three most frequently referred to ones seem to be the
In fact both NCs and BHs have been found in bulgeless galaxies. For NCs see B02; for BHs see, for example, the cases of NGC4395 [
To conclude this introduction, measurements of the demographics of the lowest-mass BHs are an important goal. Their mass distribution encodes a fossil record of the mass scale and formation efficiency of the initial BH seeds at high redshift (e.g., [
Our sample consists of 9 NCs culled from the HST
VLT/UVES spectra with high S/N and high spectral resolution have been obtained by W05. We use their velocity dispersion measurement. The properties of our sample are summarized in Table
Properties of the sample of NCs in bulgeless galaxies.
Galaxy | Type | |||||
---|---|---|---|---|---|---|
NGC 300 | SAd | 2.9 | 0.41 | |||
NGC 428 | SABm | 3.36 | 24.4 | 0.41 | ||
NGC 1042 | SABcd | 1.94 | 32 | 0.07 | ||
NGC 1493 | SBcd | 2.6 | 25 | 0.07 | ||
NGC 2139 | SABcd | 10.3 | 17 | 0.02 | ||
NGC 3423 | SAcd | 4.18 | 30 | 0.87 | ||
NGC 7418 | SABcd | 12.3 | 34 | 0.10 | ||
NGC 7424 | SABcd | 7.4 | 16 | 0.10 | ||
NGC 7793 | SAd | 7.7 | 25 | 0.15 |
The sample selection for spectroscopic follow-up technically implied a slight bias to the more luminous among the NCs. Nevertheless, we expect this sample to be a fair representation of NCs in pure disk galaxies in general, as it covers the upper
We constructed a dynamical model to estimate the mass and
We use the Jeans Anisotropic MGE (JAM) software by Cappellari [
The
The maximum allowed mass of the black hole will be obtained when a minimum of mass is present in the form of stars. From Figure
We explicitly test the effect of velocity anisotropy on the modeling results and found very little change in the results—certainly below our systematic uncertainties due to the lower limit to the mass-to-light ratio that we apply (see also [
We now plot the upper limits we have derived into figures showing existing correlations from earlier work. In these figures we typically have a comparison sample which is taken from a larger statistical study and we add a number of objects at the low-mass end from different sources in the literature. We have tried to be complete at the very lowest mass end of the relations. Further literature does exist, but typically, the BH masses exceed values of ~106
For Figure
The relation between the mass of the BH and the velocity dispersion of the spheroid around it. We plot the objects as listed in the text. The lines give the best fit of Gültekin et al. [
For Figure
The BH mass versus the spheroid mass (bulge, GC, NC). We plot the objects as listed in the text. The line indicates the best-fitting relation of H
For Figure
The mass of the BH against the Sersic index of the host bulge or disk. We plot the objects as listed in the text. The largest outliers are NGC205 (with
Figure
In Figure
The mass of the BH mass versus the NC mass. We plot the objects as listed in the text. The two full lines indicate an NC mass of
We now discuss the ways that we have obtained upper limits for the NC masses galaxy by galaxy. We strongly emphasize that we have tried to obtain
Sample of galaxies for which new properties were derived in this paper.
Galaxy | Type | Dist | Sersic | Ref | ||||
---|---|---|---|---|---|---|---|---|
group 1 | × | |||||||
NGC 300 | SAd | 2.2 | <1 | 1.1 | — | [ | ||
NGC 428 | SABm | 24.4 | 16.1 | <3 | 1.05 | — | [ | |
NGC 1042 | SABcd | 32 | 18.2 | <2.5 | 1.15 | — | [ | |
NGC 1493 | SBcd | 25 | 11.4 | <2.5 | 2.36 | — | [ | |
NGC 2139 | SABcd | 17 | 23.6 | <1.5 | 1.53 | — | [ | |
NGC 3423 | SAcd | 30 | 14.6 | <1.5 | 1.20 | — | [ | |
NGC 7418 | SABcd | 34 | 18.4 | <1.5 | — | — | [ | |
NGC 7424 | SABcd | 16 | 10.9 | <1.5 | 0.91 | — | [ | |
NGC 7793 | SAd | 25 | 3.3 | < | 1.27 | — | [ | |
group 2 | × | |||||||
NGC 4486 | E1 | 375 | 17.0 | <2 | 6.86 | [ | ||
NGC 4374 | E1 | 296 | 17.0 | <6.3 | 5.60 | [ | ||
NGC 1332 | S0 | 321 | 19.6 | <1.4 | — | — | [ | |
NGC 3031 | Sb | 143 | 4.1 | <7 | 3.26 | — | [ | |
NGC 4261 | E2 | 315 | 33.4 | <1.7 | 7.30 | [ | ||
group 3 | × | |||||||
NGC 4649 | E2 | 385 | 16.5 | <2 | 6.04 | [ | ||
NGC 3998 | S0 | 305 | 14.9 | <8.5 | — | — | [ | |
NGC 2787 | SB0 | 189 | 7.9 | <1.9 | 1.97 | — | [ | |
NGC 3379 | E0 | 206 | 11.7 | <1.4 | 4.29 | [ | ||
NGC 4342 | S0 | 225 | 18.0 | <2.5 | 5.11 | [ | ||
NGC 4291 | E2 | 242 | 25.0 | <5 | 4.02 | [ |
Galaxies for group 1 are from W05, and we here derived upper limits on the black hole mass and Sersic
NGC4486 (M87): the bright nucleus is dominated by AGN light. There is no evidence for an NC. We therefore use Figure 7 of Gebhardt and Thomas [
NGC4374 (M84): an AGN has been shown to exist by Bower et al. [
NGC4261: the central luminosity distribution is complex, with a nuclear disk and a luminous nuclear source which seems to be dominated by an AGN; at least a radio jet is present [
NGC1332: there is no firm evidence for an NC, although the surface brightness profile of Rusli et al. [
NGC3031: Devereux et al. [
For the following 6 objects no NC mass estimate was available. We therefore turned to the HST images as downloaded from the Hubble Legacy Archive. We have then used GALFIT [
NGC4649: no nuclear source is visible (as also found by [
NGC4291: we attempted the same procedure as before. However, due to a flat central surface brightness profile, our simple Sersic fit by itself produced an oversubtraction of the central flux, not allowing us to use the exact same procedure as for NGC4649. Nevertheless, the HST image clearly shows the absence of any point source in the center. We therefore assumed the same limit as before, that is, 21 mag in F814W, which results in
NGC3998: after the GALFIT fit, a clear spiral structure and a bar are seen in the residuals. The central light source was modeled as a Sersic with an effective radius of 0.2′′ and a Sersic
NGC4342: the fit with GALFIT was difficult, with 4 Sersic components in the final fit. The final solution was chosen to oversubtract the NC. Again we have a conservative upper limit of 21.85 mag corresponding to
NGC3379 (M105): the NC is visible in Gebhardt et al. [
NGC2787: this galaxy was analyzed in Peng et al. [
Note that in the galaxies NGC4486, NGC4374, and NGC3379 a luminous nuclear source is clearly seen. While this could all be AGN light, we see no way to ascertain the absence of an NC. In contrast to Graham and Spitler [
We now discuss and interpret a number of features we saw in the previous section, with the aim to discuss ideas that emerge from these figures but, to our knowledge, have not been discussed in the literature before. The ultimate aim of our study is of course to contribute to a consistent physical picture of black hole and nuclear cluster growth.
In Figure
We stress that this relation is purely observational at this stage. Due to the heterogeneous assembly of the Sersic
To venture a possible physical interpretation of the outliers from the relation we note the following: it could be that the transformation process from disk galaxy to spheroid is different in this galaxy mass regime. While BHs in massive galaxies grow during the morphological transformation process of their host galaxies, BHs in low-mass galaxies are not affected (fed) during the transformation process. It might be worthwhile exploring through simulations, whether this has to do with a possible transformation dichotomy, that is, mergers versus harassment. It is worth pointing out here that such a dichotomy does not seem to be immediately apparent from the age or metallicity profiles, as these seem not to depend on mass [
Figure
Figure
At the very high-mass end of the BH-mass range, the BH is much more massive than the NC. On the other hand, this is the region where global-to-nucleus relations hold best. This could happen through two mechanisms: (1) either the galaxies in question never had a sizable NC, possibly because their central BHs grew early on in the age of the universe, thus stopping NC growth [
Bekki and Graham [
The intermediate mass or transition regime may possibly lie between two boundaries, that is, above NC masses of
Does Figure
Discrimination between the different scenarios envisaged in the literature seems to be mostly an observational question at present. At low masses the error bars on BH measurements are typically very large, while NC masses are well measured. At high masses, BH masses are more accurate while the uncertainties for NC masses increase, due to resolution problems of the NCs above the underlying galaxies. We need both reliable BH and NC masses to see what the exact locus of points in this plot is. If there is a smooth transition, making the sequence look like a closed parenthesis, this would imply that the destruction of the NC due to the growing black hole is a slow process. If there really is a well-defined transition at
We have computed new upper limits for the masses of intermediate mass black holes in 9 pure disk galaxies with very low BH masses. We also computed upper limits to the masses of nuclear star clusters in the nuclei of galaxies with previously determined massive BHs. We plot these upper limits on the three global-to-nucleus relations In the In the
We expect further progress in the field to arise from better measurements of BH masses at the low-mass end of the
The authors thank the referee for an extensive report that significantly improved the presentation of the results in this paper, in particular on the NC upper limits. The authors acknowledge the support and hospitality of the ESO Garching office for science during the genesis of this work. N. Neumayer acknowledges support by the DFG cluster of excellence “Origin and Structure of the Universe”. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. They acknowledge the usage of the HyperLeda database (