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Register a new userDiscovery of a thin stellar stream in the SLAMS survey
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We report the discovery of a thin stellar stream - which we name the Jet stream - crossing the constellations of Hydra and Pyxis. The discovery was made in data from the SLAMS survey, which comprises deep $g$ and $r$ imaging for a $650$ square degree region above the Galactic disc performed by the CTIO Blanco + DECam. SLAMS photometric catalogues will be made publicly available. The stream is approximately 0.18 degrees wide and 10 degrees long, though it is truncated by the survey footprint. Its colour-magnitude diagram is consistent with an old, metal-poor stellar population at a heliocentric distance of approximately 29 kpc. We corroborate this measurement by identifying a spatially coincident overdensity of likely blue horizontal branch stars at the same distance. There is no obvious candidate for a surviving stream progenitor.
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We report the discovery of a narrow stellar stream crossing the constellations of Sculptor and Fornax in the Southern celestial hemisphere. The portion of the stream detected in the Data Release 1 photometry of the ATLAS survey is at least 12 degrees long, while its width is $approx$ 0.25 deg. The Color Magnitude Diagram of this halo sub-structure is consistent with a metal-poor [Fe/H] $lesssim -1.4$ stellar population located at a heliocentric distance of 20 $pm$ 2 kpc. There are three globular clusters that could tentatively be associated with the stream: NGC 7006, NGC 7078 (M15) and Pyxis, but NGC 7006 and 7078 seem to have proper motions incompatible with the stream orbit.
Mergers and tidal interactions between massive galaxies and their dwarf satellites are a fundamental prediction of the Lambda-Cold Dark Matter cosmology. These events are thought to influence galaxy evolution throughout cosmic history and to provide important observational diagnostics of structure formation. Stellar streams in the Local Group are spectacular evidence for satellite disruption at the present day. However, constructing a significant sample of tidal streams beyond our immediate cosmic neighborhood has proven a daunting observational challenge and their potential for deepening our understanding of galaxy formation has yet to be realized. Over the last decade, the Stellar Tidal Stream Survey has obtained deep, wide-field images of nearby Milky-Way analog galaxies with a network of robotic amateur telescopes, revealing for the first time an assortment of large-scale tidal structures in their halos. I discuss the main results of this project and future plans for performing dynamical studies of the discovered streams.
We report the discovery of two new candidate stellar systems in the constellation of Cetus using the data from the first two years of the Dark Energy Survey (DES). The objects, DES J0111-1341 and DES J0225+0304, are located at a heliocentric distance of ~ 25 kpc and appear to have old and metal-poor populations. Their distances to the Sagittarius orbital plane, ~ 1.73 kpc (DES J0111-1341) and ~ 0.50 kpc (DES J0225+0304), indicate that they are possibly associated with the Sagittarius dwarf stream. The half-light radius (r_h ~ 4.55 pc) and luminosity (M_V ~ +0.3) of DES J0111-1341 are consistent with it being an ultrafaint stellar cluster, while the half-light radius (r_h ~ 18.55 pc) and luminosity (M_V ~ -1.1) of DES J0225+0304 place it in an ambiguous region of size-luminosity space between stellar clusters and dwarf galaxies. Determinations of the characteristic parameters of the Sagittarius stream, metallicity spread (-2.18 < [Fe/H] < -0.95) and distance gradient (23 kpc < D_sun < 29 kpc), within the DES footprint in the Southern hemisphere, using the same DES data, also indicate a possible association between these systems. If these objects are confirmed through spectroscopic follow-up to be gravitationally bound systems and to share a Galactic trajectory with the Sagittarius stream, DES J0111-1341 and DES J0225+0304 would be the first ultrafaint stellar systems associated with the Sagittarius stream. Furthermore, DES J0225+0304 would also be the first confirmed case of an ultrafaint satellite of a satellite.
We report the discovery of a giant stellar tidal stream in the halo of NGC 4631, a nearby edge-on spiral galaxy interacting with the spiral NGC 4656, in deep images taken with a 40-cm aperture robotic telescope. The stream has two components: a bridge-like feature extended between NGC 4631 and NGC 4656 (stream_SE) and an overdensity with extended features on the opposite side of the NGC 4631 disk (stream_NW). Together, these features extend more than 85 kpc and display a clear (g-r) colour gradient. The orientation of stream_SE relative to the orientations of NGC 4631 and NGC 4656 is not consistent with an origin from interaction between these two spirals, and is more likely debris from a satellite encounter. The stellar tidal features can be qualitatively reproduced in an N-body model of the tidal disruption of a single, massive dwarf satellite on a moderately eccentric orbit (e=0.6) around NGC 4631 over $sim$ 3.5 Gyr, with a dynamical mass ratio (m1:m2) of ~40. Both modelling and inferences from the morphology of the streams indicate these are not associated with the complex HI tidal features observed between both spirals, which likely originate from a more recent, gas-rich accretion event. The detailed structure of stream_NW suggests it may contain the progenitor of the stream, in agreement with the N-body model. In addition, stream_NW is roughly aligned with two very faint dwarf spheroidal candidates. The system of dwarf galaxies and the tidal stream around NGC 4631 can provide an additional interesting case for exploring the anisotropy distribution of satellite galaxies recently reported in Local Group spiral galaxies by means of future follow-up observations.
Mergers and tidal interactions between massive galaxies and their dwarf satellites are a fundamental prediction of the Lambda-Cold Dark Matter cosmology. These events are thought to provide important observational diagnostics of nonlinear structure formation. Stellar streams in the Milky Way and Andromeda are spectacular evidence for ongoing satellite disruption. However, constructing a statistically meaningful sample of tidal streams beyond the Local Group has proven a daunting observational challenge, and the full potential for deepening our understanding of galaxy assembly using stellar streams has yet to be realised. Here we introduce the Stellar Stream Legacy Survey, a systematic imaging survey of tidal features associated with dwarf galaxy accretion around a sample of ~3100 nearby galaxies within z~0.02, including about 940 Milky Way analogues. Our survey exploits public deep imaging data from the DESI Legacy Imaging Surveys, which reach surface brightness as faint as ~29 mag/arcsec^2 in the r band. As a proof of concept of our survey, we report the detection and broad-band photometry of 24 new stellar streams in the local Universe. We discuss how these observations can yield new constraints on galaxy formation theory through comparison to mock observations from cosmological galaxy simulations. These tests will probe the present-day mass assembly rate of galaxies, the stellar populations and orbits of satellites, the growth of stellar halos and the resilience of stellar disks to satellite bombardment.
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