arXiv subjects

Emma Jarvis

Publications and source records attributed to Emma Jarvis.

5 recordsLinked to original sources

arXiv2026

Joint Modeling of GD-1 and C-19 as Old Streams

DESI observational data for the GD-1 and C-19 streams are compared to stream simulations in an evolving multi-halo potential of a Milky Way-like galaxy based on a cosmological Milky Way-like simulation. The number of subhalos decreases with time and the subhalo-stream encounter velocities rise as the Galaxy and its disk build up their mass. The streams develop from star clusters inserted at $\simeq$1 Gyr after the Big Bang and evolved for 13 Gyr to their current orbital positions. The measured velocity widths of the streams are compared to the matched simulations. Streams in a CDM subhalo population provide the best match to the velocity width, on the average, with considerable scatter. Streams younger than $\simeq$12 Gyr in CDM subhalos are insufficiently hot. Streams in the same potentials but with populations of WDM 5.5 keV subhalos are not, on the average, heated to the observed velocity widths, although some of the realizations do reach the observed levels. The stream density power spectrum measured along the length of the DESI GD-1 sample agrees with the CDM stream simulations, with 1.3 to 2.3 times more power than WDM 7 keV and 5.5 keV simulations. The simulations show that modeling specific streams from the time of the formation of their progenitor clusters is both feasible and necessary to reproduce their stream averaged kinematic properties.

astro-ph.GA↗

arXiv2026

Characterizing the GD-1 Stream with DESI DR2 Data: Thin Stream and Hot Cocoon

GD-1 is among the longest, coldest stellar streams in the Milky Way, making it an ideal target for probing dark matter substructure through dynamical heating. We present a catalog of 608 spectroscopically confirmed GD-1 members from the first three years of Dark Energy Spectroscopic Instrument (DESI) observations. This constitutes the largest homogeneous spectroscopic sample of GD-1, doubling the number of members previously available only through heterogeneous compilations combining multiple surveys with different systematics. Using these data, we derive updated stream tracks in sky position, proper motion, and radial velocity that extend over $100^\circ$ of the stream. We apply a Gaussian mixture model to decompose the stream into a dynamically cold thin component ($\sigma_V = 2.49\pm 0.28$ km s$^{-1}$, width $= 0.23\pm0.01^\circ$) and a kinematically hot cocoon ($\sigma_V = 6.13\pm0.75$ km s$^{-1}$, width $= 2.18\pm0.17^\circ$). The cocoon contains $\sim30\%$ of members and its velocity dispersion is consistent with $\sim11$ Gyr of heating by cold dark matter subhalos. We also detect a large proper motion dispersion ($41.36\pm4.98$ km s$^{-1}$) along the stream direction in the cocoon component. This feature indicates a significant line-of-sight distance spread in the cocoon, and its origin will be further explored in a forthcoming paper. These measurements demonstrate the power of DESI spectroscopy for characterizing the multi-component phase-space structure of stellar streams and constraining small-scale dark matter substructure.

astro-ph.GA↗

arXiv2026

The Kinematically Hot, Extremely Metal-Poor C-19 Stellar Stream in DESI DR2

Stellar streams are the result of a host galaxy's gravitational potential tidally disrupting satellite dwarf galaxies and globular clusters (GCs), causing them to grow leading and trailing tidal tails. The C-19 stellar stream is an extremely metal-poor stellar population, showing chemical abundance patterns characteristic of a globular cluster. However, its large velocity dispersion is difficult to reconcile with a conventional, purely baryonic, disrupting-GC progenitor. Current techniques for stream characterization are primarily applied to Gaia DR3, relying heavily on proper motion measurements. Using the Dark Energy Spectroscopic Instrument (DESI), which provides radial velocities and metallicites for over 10 million stars reaching significantly fainter magnitudes than comparable surveys, we employ a mixture model approach to jointly characterize stream populations in proper motions, radial velocities, and metallicities against a Milky Way halo background. By applying this framework to the C-19 stellar stream, we identify a total of 47 spectroscopically confirmed member stars, of which 41 are newly identified and only 6 were previously reported in the literature. In this work, we measure a velocity dispersion of $7.8^{+1.5}_{-1.3}$ km s$^{-1}$ and a mean metallicity of [Fe/H] = $-3.36^{+0.12}_{-0.10}$. We further identify a novel 'spur' feature within the stream. We conclude that our measurements are in line with previous works identifying C-19 as a 'hot', metal-poor stream. In forthcoming work, we will apply this approach to many more streams in the DESI footprint, enabling population-level comparisons with predictions from simulations.

astro-ph.GA↗

arXiv2025

SIGNALS of Giant HII Regions: A Spatially Resolved Analysis of NGC 604

Observing giant HII regions at fine spatial scales uncovers detailed structures and reveals variations in ionization, abundance, and dynamical properties of ionized gas and the effect of stellar feedback. Using emission line data of M33 observed with SITELLE as part of the Star-formation, Ionized Gas, and Nebular Abundances Legacy Survey (SIGNALS), we present maps of the principal optical emission line ratios for NGC 604, the most luminous HII region in M33. The excitation maps align well with the H$\alpha$ morphology and are clearly related to the location of the central stellar cluster and secondary stellar groups. The maps of ionization-sensitive line ratios show substantial variations across the face of NGC 604. We demonstrate that these variations are unlikely to be due to chemical inhomogeneities but are primarily caused by changes in ionization, which in turn affect the observed line ratios. We present the H$\alpha$ kinematics of the region and connect it to the excitation structure, showing how the dynamic motions influence the spatial distribution of ionized gas. We note two distinct sources identified in these excitation maps: a known supernova remnant and a previously unknown planetary nebula. Such parsec-scale features contribute only a small percentage to the overall light and would remain undetected without the use of high-resolution spatial data. Throughout the paper, we make comparisons to and raise concerns about single-aperture and long-slit spectroscopic measurements of giant HII regions, highlighting the limitations and potential inaccuracies of such methods.

astro-ph.GA↗

arXiv2024

The stability of dense cores near the Serpens South protocluster

Most stars form in clusters and groups rather than in isolation. We present $\lesssim 5^{\prime\prime}$ angular resolution ($\sim 2000$ au, or 0.01 pc) Very Large Array NH$_3$ (1,1), (2,2), and (3,3) and 1.3 cm continuum emission observations of the dense gas within the Serpens South protocluster and extended filaments to the north and south. We identify 94 dense cores using a dendrogram analysis of the NH$_3$ (1,1) integrated intensity. Gas temperatures $T_K$ and non-thermal linewidths $\sigma_\mathrm{NT}$ both increase towards the centre of the young stellar cluster, in the dense gas generally and in the cores specifically. We find that most cores (54\%) are super-virial, with gravitationally bound cores located primarily in the filaments. Cores in the protocluster have higher virial parameters by a factor $\sim 1.7$, driven primarily by the increased core $\sigma_\mathrm{NT}$ values. These cores cannot collapse to form stars unless they accrete additional mass or their core internal motions are reduced. The southern filament shows a significant velocity gradient previously interpreted as mass flow toward the cluster. We find more complex kinematics in the northern filament. We find a strong correlation between $\sigma_\mathrm{NT}$ and $T_K$, and argue that the enhanced temperatures and non-thermal motions are due to mechanical heating and interaction between the protocluster-driven outflows and the dense gas. Filament-led accretion may also contribute to the increased $\sigma_\mathrm{NT}$ values. Assuming a constant fraction of core mass ends up in the young stars, future star formation in the Serpens South protocluster will shift to higher masses by a factor $\sim 2$.

astro-ph.GA↗