The halo of M49 and its environment as traced by planetary nebulae
  The galaxy M49 (NGC 4472) is the brightest early-type galaxy in the Virgo
Cluster. It is located in Subcluster B and has an unusually blue, metal-poor
outer halo. Planetary nebulae (PNe) are excellent tracers of diffuse galaxy and
intragroup light. We present a photometric survey of PNe in the galaxy's
extended halo to characterise its PN population, as well as the surrounding
intragroup light (IGL) of the Subcluster B. PNe were identified based on their
bright [OIII]5007 \AA\ emission and absence of a broad-band continuum. We
identify 738 PNe out to a radius of 155 kpc from M49's centre from which we
define a complete sample of 624 PNe within a limiting magnitude of m_5007=28.8.
Comparing the PN number density to the broad-band stellar surface brightness
profile, we find a variation of the PN-specific frequency (alpha-parameter)
with radius. The outer halo beyond 60 kpc has a 3.2 times higher
alpha-parameter compared to the main galaxy halo, which is likely due to
contribution from the surrounding blue IGL. We use the Planetary Nebulae
Luminosity Function (PNLF) as an indicator of distance and stellar population.
Its slope, which correlates empirically with galaxy type, varies within the
inner halo. In the eastern quadrant of M49, the PNLF slope is shallower,
indicating an additional localised, bright PN population following an accretion
event, likely that of the dwarf irregular galaxy VCC1249. We also determined a
distance modulus of mu = 31.29+/-0.08 for M49, corresponding to a physical
distance of 18.1+/-0.6 Mpc, which agrees with a recent surface-brightness
fluctuations distance. The PN populations in the outer halo of M49 are
consistent with the presence of a main Sersic galaxy halo with a slight (B-V)
colour gradient of 10${}^{-4}$ mag/arcsec surrounded by intragroup light with a
very blue colour of (B-V)=0.25 and a constant surface brightness mu_V=28.0
mag/arcsec${}^2$.
