Mapping the Stellar Dynamics of M31 (original) (raw)
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Tracing the star stream through M31 using planetary nebula kinematics
Monthly Notices of The Royal Astronomical Society, 2003
We present a possible orbit for the Southern Stream of stars in M31, which connects it to the Northern Spur. Support for this model comes from the dynamics of planetary nebulae (PNe) in the disk of M31: analysis of a new sample of 2611 PNe obtained using the Planetary Nebula Spectrograph reveals ∼ 20 objects whose kinematics are inconsistent with the normal components of the galaxy, but which lie at the right positions and velocities to connect the two photometric features via this orbit. The satellite galaxy M32 is coincident with the stream both in position and velocity, adding weight to the hypothesis that the stream comprises its tidal debris.
Monthly Notices of The Royal Astronomical Society, 2006
We present a catalogue of positions, magnitudes and velocities for 3300 emission-line objects found by the Planetary Nebula Spectrograph in a survey of the Andromeda galaxy, M31. Of these objects, 2615 are found likely to be planetary nebulae (PNe) associated with M31. The survey area covers the whole of M31's disc out to a radius of 1. • 5. Beyond this radius, observations have been made along the major and minor axes, and the Northern Spur and Southern Stream regions. The calibrated data have been checked for internal consistency and compared with other catalogues. With the exception of the very central, high surface brightness region of M31, this survey is complete to a magnitude limit of m 5007 ∼ 23.75, 3.5 mag into the PN luminosity function.
Investigating the Andromeda stream - I. Simple analytic bulge-disc-halo model for M31
Monthly Notices of the Royal Astronomical Society, 2006
This paper is the first in a series which studies interactions between M31 and its satellites, including the origin of the giant southern stream. We construct accurate yet simple analytic models for the potential of the M31 galaxy to provide an easy basis for calculation of orbits in M31's halo. We use an NFW dark halo, an exponential disk, a Hernquist bulge, and a central black hole point mass to describe the galaxy potential. We constrain the parameters of these functions by comparing to existing surface brightness, velocity dispersion, and rotation curve measurements of M31. Our description provides a good fit to the observations, and agrees well with more sophisticated modeling of M31. While in many respects the parameter set is well constrained, there is substantial uncertainty in the outer halo potential and a near-degeneracy between the disk and halo components, producing a large, nearly two-dimensional allowed region in parameter space. We limit the allowed region using theoretical expectations for the halo concentration, baryonic content, and stellar M/L ratio, finding a smaller region where the parameters are physically plausible. Our proposed mass model for M31 has M bulge = 3.2 × 10 10 M ⊙ , M disk = 7.2 × 10 10 M ⊙ , and M 200 = 7.1 × 10 11 M ⊙ , with uncorrected (for internal and foreground extinction) mass-to-light ratios of M/L R = 3.9 and 3.3 for the bulge and disk, respectively. We present some illustrative test particle orbits for the progenitor of the stellar stream in our galaxy potential, highlighting the effects of the remaining uncertainty in the disk and halo masses.
Investigating the Andromeda stream - III. A young shell system in M31
Monthly Notices of the Royal Astronomical Society, 2007
Published maps of red giant stars in the halo region of M31 exhibit a giant stellar stream to the south of this galaxy, as well as a giant "shelf" to the northeast of M31's center. Using these maps, we find that there is a fainter shelf of comparable size on the western side as well. By choosing appropriate structural and orbital parameters for an accreting dwarf satellite within the accurate M31 potential model of Geehan et al. , we produce a very similar structure in an N -body simulation. In this scenario, the tidal stream produced at pericenter of the satellite's orbit matches the observed southern stream, while the forward continuation of this tidal stream makes up two orbital loops, broadened into fan-like structures by successive pericentric passages; these loops correspond to the NE and W shelves. The tidal debris from the satellite also reproduces a previously-observed "stream" of counterrotating PNe and a related stream seen in red giant stars. The debris pattern in our simulation resembles the shell systems detected around many elliptical galaxies, though this is the first identification of a shell system in a spiral galaxy and the first in any galaxy close enough to allow measurements of stellar velocities and relative distances. We discuss the physics of these partial shells, highlighting the role played by spatial and velocity caustics in the observations. We show that kinematic surveys of the tidal debris will provide a sensitive measurement of M31's halo potential, while quantifying the surface density of debris in the shelves will let us reconstruct the original mass and time of disruption of the progenitor satellite.
The kinematic footprints of five stellar streams in Andromeda's halo ★
Monthly Notices of the Royal Astronomical Society, 2008
We present a spectroscopic analysis of five stellar streams ('A', 'B', 'Cr', 'Cp' and 'D') as well as the extended star cluster, EC4, which lies within Stream 'C', all discovered in the halo of M31 from our CFHT/MegaCam survey. These spectroscopic results were initially serendipitous, making use of our existing observations from the DEep Imaging Multi-Object Spectrograph mounted on the Keck II telescope, and thereby emphasizing the ubiquity of tidal streams that account for ∼70% of the M31 halo stars in the targeted fields. Subsequent spectroscopy was then procured in Stream 'C' and Stream 'D' to trace the velocity gradient along the streams. Nine metal-rich ([Fe/H]∼-0.7) stars at v hel = −349.5 km/s, σ v,corr ∼ 5.1 ± 2.5 km/s are proposed as a serendipitous detection of Stream 'Cr', with followup kinematic identification at a further point along the stream. Six metal-poor ([Fe/H]∼-1.3) stars confined to a narrow, 15 km/s velocity bin centered at v hel = −285.6 km/s, σ v,corr = 4.3 +1.7 −1.4 km/s represent a kinematic detection of Stream 'Cp', again with followup kinematic identification further along the stream. For the cluster EC4, candidate member stars with average [Fe/H]∼-1.4 ([Fe/H] spec =-1.6), are found at v hel = −285 km/s suggesting it could be related to Stream 'Cp'. No similarly obvious cold kinematic candidate is found for Stream 'D', although candidates are proposed in both of two spectroscopic pointings along the stream (both at ∼ −400km/s). Spectroscopy near the edge of Stream 'B' suggests a likely kinematic detection at v hel ∼ −330 km/s, σ v,corr ∼ 6.9 km/s, while a candidate kinematic detection of Stream 'A' is found (plausibly associated to M33 rather than M31) with v hel ∼ −170 km/s, σ v,corr = 12.5 km/s. The low dispersion of the streams in kinematics, physical thickness, and metallicity makes it hard to reconcile with a scenario whereby these stream structures as an ensemble are related to the giant southern stream. We conclude that the M31 stellar halo is largely made up of multiple kinematically cold streams.
The Planetary Nebula System of M33
Astrophysical Journal, 2004
Fiber-coupled spectroscopy of 140 of the PN candidates confirms that M33's PN population rotates along with the old disk, with a small asymmetric drift of \~ 10km/s. Remarkably, the population's line-of-sight velocity dispersion varies little over ~4 optical disk scale lengths, with sigma_{rad}~20km/s. We show that this is due to a combination of factors, including a decline in the radial component of the velocity ellipsoid at small galactocentric radii, and a gradient in the ratio of the vertical to radial velocity dispersion. We use our data to show that the mass scale length of M33's disk is ~2.3 times larger than that of the system's IR luminosity and that the disk's V-band mass-to-light ratio changes from M/L_V ~0.3 in the galaxy's inner regions to M/L_V ~2.0 at ~9 kpc. Models in which the dark matter is distributed in the plane of the galaxy are excluded by our data. (abridged)
A New Giant Stellar Structure in the Outer Halo of M31
The Astrophysical Journal, 2004
The Sloan Digital Sky Survey has revealed an overdensity of luminous red giant stars ∼ 3 • (40 projected kpc) to the northeast of M31, which we have called Andromeda NE. The line-of-sight distance to Andromeda NE is within ∼ 50 kpc of M31; Andromeda NE is not a physically unrelated projection. Andromeda NE has a g-band absolute magnitude of ∼ −11.6 and central surface brightness of ∼ 29 mag arcsec −2 , making it nearly two orders of magnitude more diffuse than any known Local Group dwarf galaxy at that luminosity. Based on its distance and morphology, Andromeda NE is likely undergoing tidal disruption. Andromeda NE's red giant branch color is unlike that of M31's present-day outer disk or the stellar stream reported by , arguing against a direct link between Andromeda NE and these structures. However, Andromeda NE has a red giant branch color similar to that of the G1 clump; it is possible that these structures are both material torn off of M31's disk in the distant past, or that these are both part of one ancient stellar stream.
Kinematic properties of early-type galaxy haloes using planetary nebulae
Monthly Notices of The Royal Astronomical Society, 2009
We present new planetary nebulae (PNe) positions, radial velocities, and magnitudes for 6 early-type galaxies obtained with the Planetary Nebulae Spectrograph (PN.S), along with derived two-dimensional velocity and velocity dispersion fields, and the α parameters (i.e. the number of PNe per unit luminosity). We also present new deep absorption-line long-slit kinematics for 3 galaxies in the sample, obtained with the VLT/FORS2 spectrograph.
The Planetary Nebula Spectrograph survey of S0 galaxy kinematics
Astronomy & Astrophysics, 2013
Context. The origins of S0 galaxies remain obscure, with various mechanisms proposed for their formation, likely depending on environment. These mechanisms would imprint different signatures in the galaxies' stellar kinematics out to large radii, offering a method for distinguishing between them. Aims. We aim to study a sample of six S0 galaxies from a range of environments, and use planetary nebulae (PNe) as tracers of their stellar populations out to very large radii, to determine their kinematics in order to understand their origins. Methods. Using a special-purpose instrument, the Planetary Nebula Spectrograph, we observe and extract PNe catalogues for these six systems. Results. We show that the PNe have the same spatial distribution as the starlight, that the numbers of them are consistent with what would be expected in a comparable old stellar population in elliptical galaxies, and that their kinematics join smoothly onto those derived at smaller radii from conventional spectroscopy. Conclusions. The high-quality kinematic observations presented here form an excellent set for studying the detailed kinematics of S0 galaxies, in order to unravel their formation histories. We find that PNe are good tracers of stellar kinematics in these systems. We show that the recovered kinematics are largely dominated by rotational motion, although with significant random velocities in most cases.
The kinematics of 867 galactic planetary nebulae
Astronomy and Astrophysics Supplement Series, 1998
We present a compilation of radial velocities of 867 galactic planetary nebulae. Almost 900 new measurements are included. Previously published kinematical data are compared with the new high-resolution data to assess their accuracies. One of the largest samples in the literature shows evidence for a systematic velocity offset. We calculate weighted averages between all available data. Of the final values in the catalogue, 90% have accuracies better than 20 km s −1 . We use this compilation to derive kinematical parameters of the galactic differential rotation obtained from least-square fitting and to establish the Disk rotation curve; we find no significal trend for the presence of an increasing external rotation curve. We examine also the rotation of the bulge; the derived curve is consistent with a linearly increasing rotation velocity with l: we find V b,r = (9.9±1.3)l−(6.7±8.5) km s −1 . A possible steeper gradient in the innermost region is indicated.