2,922 research outputs found
Can galaxy growth be sustained through HI-rich minor mergers?
Local galaxies with specific star-formation rates (star-formation rate per
unit mass; sSFR~0.2-10/Gyr) as high as distant galaxies (z~1-3), are very rich
in HI. Those with low stellar masses, log M_star (M_sun)=8-9, for example, have
M_HI/M_star~5-30. Using continuity arguments of Peng et al. (2014), whereby the
specific merger rate is hypothesized to be proportional to the specific
star-formation rate, and HI gas mass measurements for local galaxies with high
sSFR, we estimate that moderate mass galaxies, log M_star (M_sun)=9-10.5, can
acquire sufficient gas through minor mergers (stellar mass ratios ~4-100) to
sustain their star formation rates at z~2. The relative fraction of the gas
accreted through minor mergers declines with increasing stellar mass and for
the most massive galaxies considered, log M_star (M_sun)=10.5-11, this
accretion rate is insufficient to sustain their star formation. We checked our
minor merger hypothesis at z=0 using the same methodology but now with
relations for local normal galaxies and find that minor mergers cannot account
for their specific growth rates, in agreement with observations of HI-rich
satellites around nearby spirals. We discuss a number of attractive features,
like a natural down-sizing effect, in using minor mergers with extended HI
disks to support star formation at high redshift. The answer to the question
posed by the title, "Can galaxy growth be sustained through \HI-rich minor
mergers?", is maybe, but only for relatively low mass galaxies and at high
redshift.Comment: 6 pages, 3 figures; in final acceptance by A&
Dissecting the complex environment of a distant quasar with MUSE
High redshift quasars can be used to trace the early growth of massive
galaxies and may be triggered by galaxy-galaxy interactions. We present MUSE
science verification data on one such interacting system consisting of the
well-studied z=3.2 PKS1614+051 quasar, its AGN companion galaxy and bridge of
material radiating in Lyalpha between the quasar and its companion. We find a
total of four companion galaxies (at least two galaxies are new discoveries),
three of which reside within the likely virial radius of the quasar host,
suggesting that the system will evolve into a massive elliptical galaxy by the
present day. The MUSE data are of sufficient quality to split the extended
Lyalpha emission line into narrow velocity channels. In these the gas can be
seen extending towards each of the three neighbouring galaxies suggesting that
the emission-line gas originates in a gravitational interaction between the
galaxies and the quasar host. The photoionization source of this gas is less
clear but is probably dominated by the two AGN. The quasar's Lyalpha emission
spectrum is double-peaked, likely due to absorbing neutral material at the
quasar's systemic redshift with a low column density as no damping wings are
present. The spectral profiles of the AGN and bridge's Lyalpha emission are
also consistent with absorption at the same redshift indicating this neutral
material may extend over > 50 kpc. The fact that the neutral material is seen
in the line of sight to the quasar and transverse to it, and the fact that we
see the quasar and it also illuminates the emission-line bridge, suggests the
quasar radiates isotropically and any obscuring torus is small. These results
demonstrate the power of MUSE for investigating the dynamics of interacting
systems at high redshift.Comment: 9 pages, 6 figures, published in MNRA
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