A Survey of Satellite Galaxies around NGC 4258

TL;DR

This survey of satellite galaxies around NGC 4258 combines new spectroscopic data with existing spectra to analyze satellite membership, distribution, and properties, revealing a diverse satellite population with unique color and star formation characteristics.

Contribution

It provides the first comprehensive spectroscopic survey of NGC 4258 satellites, including new data and analysis of their distribution, mass profile, and properties, highlighting differences from the Milky Way and M31.

Findings

Total mass within 200 kpc is 1.8e12 Msun.

Satellite distribution appears random, not disk-aligned.

Many probable satellites are blue and star-forming.

Abstract

We conduct a survey of satellite galaxies around the nearby spiral NGC 4258 by combining spectroscopic observations from the Apache Point Observatory 3.5-meter telescope with SDSS spectra. New spectroscopy is obtained for 15 galaxies. Of the 47 observed objects, we categorize 8 of them as probable satellites, 8 as possible satellites, and 17 as unlikely to be satellites. We do not speculate on the membership of the remaining 14 galaxies due to a lack of velocity and distance information. Radially integrating our best fit NFW profile for NGC 4258 yields a total mass of 1.8e12 Msun within 200 kpc. We find that the angular distribution of the satellites appears to be random, and not preferentially aligned with the disk of NGC 4258. In addition, many of the probable satellite galaxies have blue u-r colors and appear to be star-forming irregulars in SDSS images; this stands in contrast to the low number of blue satellites in the Milky Way and M31 systems at comparable distances.