22 research outputs found
Discovery of a Giant Stellar Tidal Stream Around the Disk Galaxy NGC 4013
We report the discovery of a giant, loop-like stellar structure around the
edge-on spiral galaxy NGC 4013. This arcing feature extends 6 arcmin (~26 kpc
in projected distance) northeast from the center and 3 arcmin (~=12 kpc) from
the disk plane; likely related features are also apparent on the southwest side
of the disk, extending to 4 arcmin (~17 kpc). The detection of this low
surface-brightness muR= 27.0+0.3-0.2 mag/sqarcsec) structure is independently
confirmed in three separate datasets from three different telescopes.
Although its true three dimensional geometry is unknown, the sky- projected
morphology of this structure displays a match with the theoretical predictions
for the edge-on, projected view of a stellar tidal streams of a dwarf satellite
moving in a low inclined (~25deg), nearly circular orbit. Using the recent
model of the Monoceros tidal stream in the Milky Way by Penarrubia et al. as
template, we find that the progenitor system may have been a galaxy with an
initial mass 6*10^8 Msun, of which current position and final fate is unknown.
According to this simulation, the tidal stream may be approximately ~2.8 Gyr of
age.
Our results demonstrate that NGC 4013, previously considered a prototypical
isolated disk galaxy in spite of having one of the most prominent HI warps
detected thus far, may have in fact suffered a recent minor merger. This
discovery highlights that undisturbed disks at high surface brightness levels
in the optical but warped in HI maps may in fact reveal complex signatures of
recent accretion events in deep photometric surveys.Comment: Comments: LaTeX, ApJ preprint style, 21 pages, 6 figures (reduced
quality), ApJ accepted. A high resolution version of the paper in addition to
a full version of the colour image of NGC 4013 can be found at
http://www.cosmotography.com/images/iac/ngc4013.html . Replaced to match
accepted version after revisions following referee's repor
The ghost of a dwarf galaxy: fossils of the hierarchical formation of the nearby spiral galaxy NGC 5907
We present an extragalactic perspective of an extended stellar tidal stream
wrapping around the edge-on, spiral galaxy NGC 5907. Our deep images reveal for
the first time a large scale complex of arcing loops that is an excellent
example of how a low-mass satellite accretion can produce an interwoven,
rosette-like structure of debris dispersed in the halo of its host galaxy. The
existence of this structure, which has probably formed and survived for several
Gigayears, confirms that halos of spiral galaxies in the Local Universe may
still contain a significant number of galactic fossils from their hierarchical
formation. To examine the validity of the external accretion scenario, we
present N-body simulations of the tidal disruption of a dwarf galaxy-like
system in a disk galaxy plus dark halo potential that demonstrate that most of
the observed tidal features observed in NGC 5907 can be explained by a single
accretion event. Unfortunately, with no kinematic data and only the projected
geometry of the stream as constraint, the parameters of our model are
considerably degenerate and, for now, must be considered illustrative only.
Interestingly, NGC 5907 has long been considered a prototypical example of a
warped spiral in relative isolation. The presence of an extended tidal stream
challenges this picture and suggests that the gravitational perturbations
induced by the stream progenitor may be the cause for the warp. The detection
of an old, complex tidal stream in a nearby galaxy with rather modest
instrumentation points to the viability of surveys to find extragalactic tidal
substructures around spiral galaxies in the Local Volume (< 15 Mpc) -- with the
prospect of obtaining a census with enough statistical significance to be
compared with cosmological simulations.Comment: Accepted for publication in The Astrophysical Journal. High
resolution version of the paper, full colour version of the NGC 5907 tidal
stream image, movie of the N-body model and IAC press release can be found
at: http://www.cosmotography.com/images/small_ring_ngc5907.htm
Imaging of NGC 5907's stellar stream
We have obtained deep g, r, and i-band Subaru and ultra-deep 3.6 ÎŒm IRAC images of parts of the multiply-wrapped stellar stream around the nearby edge-on galaxy NGC 5907. We have fitted the surface brightness measurements of the stream with FSPS stellar population synthesis models to derive the metallicity and age of the brightest parts of the stream. The resulting relatively high metallicity ([Fe/H] = â0.3) is consistent with a major merger scenario but a satellite accretion event cannot be ruled out
A Petal of the Sunflower: Photometry of the Stellar Tidal Stream in the Halo of Messier 63 (NGC 5055)
We present surface photometry of a very faint, giant arc feature in the halo
of the nearby spiral galaxy NGC 5055 (M63) that is consistent with being a part
of a stellar stream resulting from the disruption of a dwarf satellite galaxy.
This faint feature was first detected in early photographic studies by van der
Kruit (1979); more recently by Mart\'inez-Delgado et al. (2010) and as
presented in this work, the loop has been realized to be the result of a recent
minor merger through evidence obtained by deep images taken with a telescope of
only 0.16 m aperture. The stellar stream is confirmed in additional images
taken with the 0.5 m of the BlackBird Remote Observatory and the 0.8 m of the
McDonald Observatory. This low surface brightness structure around the disk of
the galaxy extends ~29 kpc from its center, with a projected width of 3.3 kpc.
The stream's morphology is consistent with that of the visible part of a
"great-circle" stellar stream originating from the accretion of a ~10^8 M_sun
dwarf satellite in the last few Gyr. The progenitor satellite's current
position and fate are not conclusive from our data. The color of the stream's
stars is consistent with Local Group dwarfs and is similar to the outer regions
of M63's disk and stellar halo. We detect other low surface brightness
"plumes"; some of these may be extended spiral features related to the galaxy's
complex spiral structure and others may be tidal debris associated with the
disruption of the galaxy's outer stellar disk as a result of the accretion
event. We differentiate between features related to the tidal stream and faint,
blue features in the outskirts of the galaxy's disk previously detected by the
GALEX satellite. With its highly warped HI gaseous disk (~20 deg), M63
represents one of several examples of an isolated spiral galaxy with a warped
disk showing strong evidence of an ongoing minor merger.Comment: 16 pages, 10 figures, 3 tables, Accepted for publication in The
Astronomical Journa
Unveiling the nature of M94's (NGC4736) outer region: a panchromatic perspective
We have conducted a deep multi-wavelength analysis (0.15-160 mum) to study
the outer region of the nearby galaxy M94. We show that the non-optical data
support the idea that the outskirts of this galaxy is not formed by a closed
stellar ring (as traditionally claimed in the literature) but by a spiral arm
structure. In this sense, M94 is a good example of a Type III (anti-truncated)
disk galaxy having a very bright outer disk. The outer disk of this galaxy
contains ~23% of the total stellar mass budget of the galaxy and contributes
~10% of the new stars created showing that this region of the galaxy is active.
In fact, the specific star formation rate of the outer disk (~0.012 Gyr^{-1})
is a factor of ~2 larger (i.e. the star formation is more efficient per unit
stellar mass) than in the inner disk. We have explored different scenarios to
explain the enhanced star formation in the outer disk. We find that the inner
disk (if considered as an oval distortion) can dynamically create a spiral arm
structure in the outer disk which triggers the observed relatively high star
formation rate as well as an inner ring similar to what is found in this
galaxy.Comment: Accepted for publication in ApJ, 15 pages, 9 figure