Relations Between Supermassive Black Hole Mass, Host Galaxy
Morphology and Host Galaxy Mass
Neslihan AlanA,∗ & Şivan DuranA,∗∗
A
Istanbul University, Faculty of Sciences, Department of Astronomy and Space Sciences, 34119, Istanbul, Turkey
[∗neslihan.alan, ∗∗duransivan]@gmail.com
Abstract
We present the relation between supermassive black hole (M•) and host galaxy masses (MGal )
in terms of the host galaxy morphology using data taken from Nair & Abraham (2010). Since
the data don’t contain the black hole masses, we calculate them using the M•–σ (σ: velocity
dispersion) relation given by Gültekin et al. (2009). We find a strong linear relation between
black hole and host galaxy masses. In addition, there is a finding which shows that the most
massive black holes are contained by the elliptical galaxies and also these galaxies tend to
be more massive than the other galaxies. Depending on these results, we discuss that these
massive ellipticals could probably be formed or evaluated by mergers.
Introduction
Relations between the masses of supermassive black holes, located at the centre
of galaxies with a mass from ∼ 103 to ∼ 109M, and properties of host galaxies,
such as morphologies, masses, absolute magnitudes, etc. possess information about
the evolution of galaxies. Since massive black holes have strong gravitational effects
on the nearby stars, velocity dispersions of these stars will be changed significantly.
Thus, stellar velocity dispersions are used as a measurement of the black hole masses
(Gültekin et al., 2009).
There are various galaxies with different properties. They are classified for a better
understanding of how they formed and evolved or what kind of properties they have in Figure 2: The MGal–M• relation for 12,773 galaxies. The colour bar indicates the number of galaxies.
While big dots show mean values for each interval (see the text), dashed line is the linear fit through
common. Hubble ordered galaxies in their appearances such as eccentricities, smooth these points.
light profiles, spiral arms, central bulges, and irregular or peculiar morphologies. Based
on these features the Hubble sequence or Hubble tuning-fork diagram was made as
seen in Figure 1.
We computed masses of 12,733 galaxies chosen from Nair & Abraham (2010). According to our computations we found that the massive elliptical galaxies have the
most massive black holes and also their masses are greater than spiral ones as shown
in Figure 3.
Results and Discussion
Figure 1: The Hubble tuning-fork diagram.
Elliptical galaxies are named due to their ellipsoidal shapes and show no bulge- or
bar-like structures. They are old, red, and contain little gas and dust. Lenticulars
are an intermediate class between ellipticals and spirals. They have an elliptical-like
smooth light profile, a spiral-like bulge and thin disk. In spite of ellipticals, morphology
of spiral galaxies are more complicated. They have a thin, rotating disk with spiral
arms, often a bar and a central bulge. They are usually young, blue and contain star
formation regions, a lot of gas and dust. Irregular galaxies show no prominent bulge
or disk and their appearance is patchy. Whereas spirals and irregulars are the class of
late-type galaxies, ellipticals and lenticulars are referred to as early-type galaxies (Mo,
van den Bosch & White, 2003).
Data and Sample
In this study, we used data taken from Nair & Abraham (2010). The data contain
masses, velocity dispersions, the numerical Hubble stages (T-Types), colours, ages,
etc. except black hole masses. In order to determine black hole masses we used the
M•–σ relation given by Gültekin et al. (2009).
The data have 14,034 galaxies in total. However the number of galaxies with mass
determination is 13,802. 335 of these galaxies have unknown T-Types thus we omitted
335 galaxies. Furthermore, we needed to eliminate the galaxies which have the black
hole mass greater than its mass. Thus, we finally have 12,773 galaxies as a final sample. Our final sample is shown in Figure 2. The figure also demonstrates the MGal –M•
relation in terms of galaxy numbers.
Black Hole Mass Estimation
Determination of black hole masses is not straightforward. Various methods are used
in order to estimate black hole masses in the literature. Star and gas motions are affected by the supermassive black holes in galaxy bulges so that velocity dispersions
are a measurement of the black hole masses.
We used the following equation given by Gültekin et al. (2009) to determine black
hole masses:
−1 4.24
8.12
M• = 10 M × (σ/200 km s ) .
Figure 3: Same as Figure 2 but the colour bar indicates galaxy morphologies.
As mentioned before, we found a linear relation between log MGal and log M• in the
5 ≤ log M•(M) ≤ 9.5 range. We divided this range into 5 bins with a mass of 0.5M.
Mean log MGal and log M• are calculated for each bin and these bins are shown as big
dots in Figure 2. 1-σ standard deviations of the masses for each bin are given as error
bars in the figure. We fitted a linear model through these mean values and found the
following equation:
log M• = 2.29 × log MGal − 17.19.
Elliptical galaxies are generally found at the centre of the galaxy clusters (Laine et
al., 2003). Due to their places in the galaxy clusters, ellipticals inevitably interact with
other galaxies. These interactions should increase the evolution speed of ellipticals.
One can ask if the massive ellipticals in the galaxy clusters formed or evolved, when
outer galaxies had been gathered around the centre of the cluster by the gravitational
interactions.
References
Gültekin K., et al., 2009, ApJ, 698, 198
Laine S., van der Marel R. P., Lauer T. R., Postman M., O’Dea C. P., Owen F. N., 2003, AJ, 125, 478
Mo H., van den Bosch F., White S., Galaxy Formation and Evolution, Cambridge University Press,
June 2010, ISBN: 9780521857932
Nair P. B. & Abraham R. G., 2010, ApJS, 186, 427