NGC 1277: A Massive Compact Relic Galaxy in the Nearby Universe

Abstract

As early as 10 Gyr ago, galaxies with more than 10 11 M ⊙ in stars already existed. While most of these massive galaxies must have subsequently transformed through on-going star formation and mergers with other galaxies, a small fraction ( 0.1%) may have survived untouched till today. Searches for such relic galaxies, useful windows to explore the early Universe, have been inconclusive to date: galaxies with masses and sizes like those observed at high redshift (M ⋆ 10 11 M ⊙ ; R e 1.5 kpc) have been found in the local Universe, but their stars are far too young for the galaxy to be a relic galaxy. This paper explores the first case of a nearby galaxy, NGC1277 (at a distance of 73 Mpc in the Perseus galaxy cluster), which fulfills many criteria to be considered a relic galaxy. Using deep optical spectroscopy, we derive the star formation history along the structure of the galaxy: the stellar populations are uniformly old (>10 Gyr) with no evidence for more recent star formation episodes. The metallicity of their stars is super-solar ([Fe/H]=0.20±0.04 with a smooth decline towards the outer regions) and alpha enriched ([α/Fe]=0.4±0.1). This suggests a very short formation time scale for the bulk of stars of this galaxy. This object also rotates very fast (V rot ∼300 km/s) and has a large central velocity dispersion (σ>300 km/s). NGC1277 allows the explorations in full detail of properties such as the structure, internal dynamics, metallicity and initial mass function at ∼10-12 Gyr back in time when the first massive galaxies were built.

Towards a census of supercompact massive galaxies in the Kilo Degree Survey

“…Compact candidates also present lower axis ratios than normal galaxies. These elongated shapes are common in massive compact galaxies, both at high-z (van der Wel et al 2011;Buitrago et al 2013), and at lower redshifts (Trujillo et al , 2014.…”

“…The yellow line with lighter yellow region plot abundances for compacts in the COSMOS area (Damjanov et al 2015a Taylor et al (2010) are shown here as upper limits (see red and cyan points with arrows). The blue triangle is for the lower limit at z ∼ 0 provided by Trujillo et al (2014). Orange and red lines plot abundances of relic galaxies from semi-analytical models (SAMs), based on Millennium N-body simulations (Quilis & Trujillo 2013).…”

“…Recently there have been some efforts to search for massive compact galaxies at low redshifts (Trujillo et al 2009;Taylor et al 2010;Valentinuzzi et al 2010;Shih & Stockton 2011;Trujillo et al 2012;Poggianti et al 2013a;Poggianti et al 2013b;Damjanov et al 2013Damjanov et al , 2014Damjanov et al , 2015aSaulder et al 2015) and investigate further their dynamical and stellar population properties, as well as the role of environment on their properties (e.g. Ferré-Mateu et al 2012;Läsker et al 2013;Ferré-Mateu et al 2015;Trujillo et al 2014;Yıldırım et al 2015;Damjanov et al 2015b;Stringer et al 2015;Wellons et al 2015a). …”

Discovery of five low-luminosity active galactic nuclei at the centre of the Perseus cluster

“…The compact lenticular galaxy, NGC 1277, was found by van den Bosch et al (2012) to have an over-massive black hole of 1.7 × 10 10 M , which corresponds to 14 percent of the total stellar mass of that galaxy. The fraction is much larger than the typical value (0.1 percent) found in a normal massive galaxy (e.g.…”

“…Recently, the early-type galaxy NGC 1277 in the Perseus cluster received much attention because, according to stellar kinematics observations, it most likely hides an over-massive black hole of ∼10 10 M (van den Bosch et al 2012;Yıldırım et al 2015). Galaxies with the most massive black holes are interesting on their own, because they may serve as probes for black hole formation models (Khan et al 2015, and references therein), may indicate capture of a runaway black hole (Shields & Bonning 2013), and may constrain black hole-galaxy co-evolution models (Croton et al 2006;Somerville et al 2008).…”