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Largest Observed SMBH In The Compact Lenticular Galaxy NGC1277

10/01/2013

It is a now just over a decade since the supermassive black hole (SMBH) paradigm began to take weight in the astronomical community. The paradigm essentially consists of the observational confirmation that our Galaxy, and many others, harbour an extremely massive object within the core nucleus (Schödel et al. 2002). Within the paradigm sits a very slight detail: the central SMBH rarely exceeds 0.1% of the host galaxy’s mass (Häring et al. 2004; Gültekin et al. 2009; Sani et al. 2011). However, for a few very select galaxies the central SMBH mass can exceed upwards of 10% of the host galaxy’s total mass e.g. NGC4486B (Magorrian et al. 2009), Henize 2-10 (Reines et al. 2011) and OJ 287. Recently, in November of last year, the largest observed fractional SMBH was measured, surpassing all the previous observed holders.

Fig. 1: Optical Hubble Space Telescope image of the compact lenticular galaxy NGC1277. (Credit: Hubble Space Telescope)

Fig. 1: Optical Hubble Space Telescope image of the compact lenticular galaxy NGC1277. (Credit: Hubble Space Telescope)

Sitting at approximately 73Mpc away, the lenticular* galaxy, rather forgettably titled “NGC 1277”, is thought to be a staggering ~14% supermassive black hole (van den Bosch et al. 2012). Hopefully the more eagle eyed readers amongst you will now be beginnign to wonder just how a black hole is measured. The answer is quite simple: spatially resolved stellar and/or gas kinematics within the region known as the “sphere-of-influence”; where the mass of the central black hole dominates the gravitational potential. Essentially, measuring and observing how objects move within the central region. The faster, and perhaps the more elliptical, the movement of the gas, dust and stars around the central region: the greater the mass of the central SMBH (Djurić et al. 2010).

N.B.* Lenticular refers to galaxies which are visually similar in characteristics and morphology to both spiral (Binney & Merrifield 1998), like the Andromeda galaxy, and elliptical galaxies (to varying degrees), an intermediate Hubble-type if you will.

However, van den Bosch (2012) seemed like they were on the hunt for only the most massive. So how is this done? Firstly, van den Bosch et al. (2012) selected galaxies that were likely to have a very dominant Galactic mass fractions within the central core. This is done by measuring two key parameters: velocity dispersion, σc, and half-light ratio, Re, K; where the larger the σ and the smaller the Re, value, the better. These galaxies were ARK90, NGC1270, NGC1277, UGC 1859,UGC 2698 and MRK1216, each with velocity dispersion values of between 350-410 km s-1 and half-light ratios of between 1.6kpc and 2.7kpc. These six galaxies targeted were observed with the Marcario Low Resolution Spectrograph (Hill et al. 1998) on the Hobby-Eberly Telescope (HET) as part of a large survey program known as HETMGS, and selected from the Two Micron All Sky Survey (2MASS) extended source catalogue (Jarrett et al. 2000) that are expected to have the largest sphere-of-influence.

Using observationally obtained measurements of the velocity dispersion and the half-light ratio, van den Bosch et al. (2012) focused on NGC1277, a galaxy 73Mpc from the Milky Way in the Perseus constellation with a stellar population older than ≳ 8Gyr. NGC 1277 was first observed in Ireland by the astronomer Lawrence Parsons in 1875. NGC1277 had a specific velocity disperson, σ = 403 ± 4 km s-1 and a half-ligh t ratio of Re, K = 1.6 kpc. These values lend itself to the possibility that the mass of the central SMBH is quite large!

These parameters can then be used to find the mass of the black hole by fitting a self-consistent Schwarzschild model; see [http://mpia-hd.mpg.de/~bosch/Schwarzschild…] for further details] (Schwarzschild 1972) to spatially resolved spectroscopy and high resolution imaging. Conveniently for van den Bosch et al. (2012), archival Hubble Space Telescope (HST) imaging is available for one of these six dense galaxies, NGC1277 (and can be seen in the greyscale image of Fig. 1, at the top of this post).

van den Bosch et al. (2012) NGC1277 obtained a value of 14% mass fraction value, as a percentage of the total stellar mass (1.2±0.4 ×1011Solar Mass), where the central black hole component was measured at 1.7±0.3 ×1010Solar Mass, making the black hole at the centre of NGC1277 one of the largest to ever be dynamically confirmed in the known Universe.

N.B. The HET Massive Galaxy Survey has allowed van den Bosch and his team to find galaxies with extremely big black holes and they are currently following those up with the Calor Alto 3.5m, Harlan J. Smith, Keck, Gemini and Hubble Space Telescopes.

Journal References:

  • van den Bosch, R.C. E.; Gebhardt, K.; Gültekin, K.; et al. (2012). An Over-Massive Black Hole In The Compact Lenticular Galaxy: NGC1277Nature, 491 (7426): pp. 729-731.
  • McConnell, N. J. et al. (2011) Two 10-Billion Solar Mass Black Holes At The Centres Of Giant Elliptical Galaxies. Nature 480: pp.215–218.
  • Häring, N. & Rix, H.-W. (2004) On The Black Hole Mass-Bulge Mass Relation. The Astrophys. Jrnl. 604, L89–L92.

Suggested Further Reading:

  • Dr. Remco van den Bosch (Max Planck Institut für Astronomie, Heidelberg) “An Over-Massive Black Hole in the Compact Lenticular Galaxy NGC1277”: [http://mpia.de/~bosch/blackholes.html].
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