Site Map
Contacts
Follow us on Facebook Follow us on Twitter YouTube channel
Centro de Astrofísica da Universidade do Porto

NGC765 - A disturbed HI giant

A. M. P. Portas, E. Brinks, M. E. Filho, A. Usero, E. M. Dyke, P.-E. Belles

Abstract
We present HI spectral line and radio-continuum Very Large Array (VLA) data of the galaxy NGC765, complemented by optical and Chandra X-ray maps. NGC765 has the largest HI-to-optical ratio known to date of any spiral galaxy and one of the largest known HI discs in absolute size with a diameter of 240 kpc measured at a surface density of 2 × 1019 atom cm -2. We derive a total HI mass of MHI = 4.7 × 1010 M, a dynamical mass of Mdyn ∼ 5.1 × 1011 M and an HI mass-to-luminosity ratio of MHI/LB = 1.6, making it the nearest and largest 'crouching giant'. Optical images reveal evidence of a central bar with tightly wound low-surface brightness spiral arms extending from it. Radio-continuum (L1.4 GHz = 1.3 × 1021 W Hz-1) and X-ray (LX ≈ 1.7 × 1040 erg s-1) emission is found to coincide with the optical core of the galaxy, compatible with nuclear activity powered by a low-luminosity AGN. We may be dealing with a galaxy that has retained in its current morphology traces of its formation history. In fact, it may still be undergoing some accretion, as evidenced by the presence of HI clumps the size (< 10 kpc) and mass (108-109 M) of small (dIrr) galaxies in the outskirts of its HI disc and by the presence of two similarly sized companions.

Keywords
galaxies: evolution - galaxies: individual: NGC 765 - galaxies: individual: UGC1453 - galaxies: interactions - galaxies: kinematics and dynamics - galaxies: structure

Monthly Notices of the Royal Astronomical Society
Volume 407, Page 1674
September 2010

>> PDF>> ADS>> DOI

Institute of Astrophysics and Space Sciences

Institute of Astrophysics and Space Sciences (IA) is a new but long anticipated research infrastructure with a national dimension. It embodies a bold but feasible vision for the development of Astronomy, Astrophysics and Space Sciences in Portugal, taking full advantage and fully realizing the potential created by the national membership of the European Space Agency (ESA) and the European Southern Observatory (ESO). IA resulted from the merging the two most prominent research units in the field in Portugal: the Centre for Astrophysics of the University of Porto (CAUP) and the Center for Astronomy and Astrophysics of the University of Lisbon (CAAUL). It currently hosts more than two-thirds of all active researchers working in Space Sciences in Portugal, and is responsible for an even greater fraction of the national productivity in international ISI journals in the area of Space Sciences. This is the scientific area with the highest relative impact factor (1.65 times above the international average) and the field with the highest average number of citations per article for Portugal.

Proceed on CAUP's website|Go to IA website