Exploring the origin of ultra-diffuse galaxies in clusters from their primordial alignment

We find that the minor axes of the ultra-diffuse galaxies (UDGs) in Abell 2634 tend to be aligned with the major axis of the central dominant galaxy, at a $\gtrsim 95\%$ confidence level. This alignment is produced by the bright UDGs with the absolute magnitudes $M_r<-15.3$ mag, and outer-region UDGs with $R>0.5R_{200}$. The alignment signal implies that these bright, outer-region UDGs are very likely to acquire their angular momenta from the vortices around the large-scale filament before they were accreted into A2634, and form their extended stellar bodies outside of the cluster; in this scenario, the orientations of their primordial angular momenta, which are roughly shown by their minor axes on the images, should tend to be parallel to the elongation of the large-scale filament. When these UDGs fell into the unrelaxed cluster A2634 along the filament, they could still preserve their primordial alignment signal before violent relaxation and encounters. These bright, outer-region UDGs in A2634 are very unlikely to be the descendants of the high-surface-brightness dwarf progenitors under tidal interactions with the central dominant galaxy in the cluster environment. Our results indicate that the primordial alignment could be a useful probe of the origin of UDGs in large-scale structures.Comment: Accepted for publication in MNRAS Lette

VLA Imaging of H i-bearing Ultra-Diffuse Galaxies from the ALFALFA Survey

Ultra-diffuse galaxies have generated significant interest due to their large optical extents and low optical surface brightnesses, which challenge galaxy formation models. Here we present resolved synthesis observations of 12 H i-bearing ultra-diffuse galaxies (HUDs) from the Karl G. Jansky Very Large Array (VLA), as well as deep optical imaging from the WIYN 3.5-meter telescope at Kitt Peak National Observatory. We present the data processing and images, including total intensity H i maps and H i velocity fields. The HUDs show ordered gas distributions and evidence of rotation, important prerequisites for the detailed kinematic models in Mancera Pi˜na et al. (2019b). We compare the H i and stellar alignment and extent, and find the H i extends beyond the already extended stellar component and that the H i disk is often misaligned with respect to the stellar one, emphasizing the importance of caution when approaching inclination measurements for these extreme sources. We explore the H i mass-diameter scaling relation, and find that although the HUDs have diffuse stellar populations, they fall along the relation, with typical global H i surface densities. This resolved sample forms an important basis for more detailed study of the H i distribution in this extreme extragalactic population

VLA Imaging of H I-bearing Ultra-diffuse Galaxies from the ALFALFA Survey

Ultra-diffuse galaxies have generated significant interest due to their large optical extents and low optical surface brightnesses, which challenge galaxy formation models. Here we present resolved synthesis observations of 12 H i-bearing ultra-diffuse galaxies (HUDs) from the Karl G. Jansky Very Large Array (VLA), as well as deep optical imaging from the WIYN 3.5-meter telescope at Kitt Peak National Observatory. We present the data processing and images, including total intensity H i maps and H i velocity fields. The HUDs show ordered gas distributions and evidence of rotation, important prerequisites for the detailed kinematic models in Mancera Pi˜na et al. (2019b). We compare the H i and stellar alignment and extent, and find the H i extends beyond the already extended stellar component and that the H i disk is often misaligned with respect to the stellar one, emphasizing the importance of caution when approaching inclination measurements for these extreme sources. We explore the H i mass-diameter scaling relation, and find that although the HUDs have diffuse stellar populations, they fall along the relation, with typical global H i surface densities. This resolved sample forms an important basis for more detailed study of the H i distribution in this extreme extragalactic population

MIGHTEE-Hi: Evolution of Hi Scaling Relations of Star-forming Galaxies at z &lt; 0.5*

We present the first measurements of H I galaxy scaling relations from a blind survey at z > 0.15. We perform spectral stacking of 9023 spectra of star-forming galaxies undetected in H I at 0.23 < z < 0.49, extracted from MIGHTEE-H I Early Science data cubes, acquired with the MeerKAT radio telescope. We stack galaxies in bins of galaxy properties (stellar mass M *, star formation rateSFR, and specific star formation rate sSFR, with sSFR ≡ M */SFR), obtaining ≳5σ detections in most cases, the strongest H I-stacking detections to date in this redshift range. With these detections, we are able to measure scaling relations in the probed redshift interval, finding evidence for a moderate evolution from the median redshift of our sample z med ~ 0.37 to z ~ 0. In particular, low-M * galaxies ( {\mathrm{log}}_{10}({M}_{* }/{M}_{\odot })\sim 9 )experienceastrongHIdepletion( 0.5dexinlog10(MHI/M⊙) ), while massive galaxies ( {\mathrm{log}}_{10}({M}_{* }/{M}_{\odot })\sim 11$ ) keep their H I mass nearly unchanged. When looking at the star formation activity, highly star-forming galaxies evolve significantly in M H I (f H I, where f H I ≡ M H I/M *) at fixed SFR (sSFR), while at the lowest probed SFR (sSFR) the scaling relations show no evolution. These findings suggest a scenario in which low-M * galaxies have experienced a strong H I depletion during the last ~5 Gyr, while massive galaxies have undergone a significant H I replenishment through some accretion mechanism, possibly minor mergers. Interestingly, our results are in good agreement with the predictions of the SIMBA simulation. We conclude that this work sets novel important observational constraints on galaxy scaling relations

The Odd Dark Matter Halos of Isolated Gas-Rich Ultra-Diffuse Galaxies

We analyze circular velocity profiles of seven ultra-diffuse galaxies (UDGs) that are isolated and gas-rich. Assuming that the dark matter halos of these UDGs have a modified Navarro-Frenk-White (NFW) density profile with a constant density core, the inferred halo concentrations are systematically lower than the cosmological median, even as low as $-0.6$ dex (about $5\sigma$ away) in some cases. Alternatively, similar fits can be obtained with a density profile that scales roughly as $1/r^2$ for radii larger than a few $\rm kpc$. Both solutions require the radius where the halo circular velocity peaks ($R_{\rm max}$) to be much larger than the median expectation. Surprisingly, we find an overabundance of such large $R_{\rm max}$ halos in the IllustrisTNG dark matter-only simulations compared to the Gaussian expectation. These halos form late and have higher spins compared to median halos of similar masses. The inner densities of the most extreme among these late-forming halos are higher than their NFW counterparts, leading to a $\sim 1/r^2$ density profile. However, the two well-resolved UDGs in our sample strongly prefer lower dark matter densities in the center than the simulated ones. Comparing to IllustrisTNG hydrodynamical simulations, we also find a tension in getting both low enough circular velocities and high enough halo mass to accommodate the measurements. Our results indicate that the gas-rich UDGs present a significant challenge for galaxy formation models.Comment: 17 pages, 14 figure

The baryonic specific angular momentum of disc galaxies

Aims. Specific angular momentum (the angular momentum per unit mass, j = J/M) is one of the key parameters that control the evolution of galaxies, and it is closely related with the coupling between dark and visible matter. In this work, we aim to derive the baryonic (stars plus atomic gas) specific angular momentum of disc galaxies and study its relation with the dark matter specific angular momentum. Methods. Using a combination of high-quality H 

No need for dark matter: resolved kinematics of the ultra-diffuse galaxy AGC 114905

We present new H I interferometric observations of the gas-rich ultra-diffuse galaxy AGC 114905, which previous work, based on low-resolution data, identified as an outlier of the baryonic Tully–Fisher relation. The new observations, at a spatial resolution ∼2.5 times higher than before, reveal a regular H I disc rotating at about 23 km s−1. Our kinematic parameters, recovered with a robust 3D kinematic modelling fitting technique, show that the flat part of the rotation curve is reached. Intriguingly, the rotation curve can be explained almost entirely by the baryonic mass distribution alone. We show that a standard cold dark matter halo that follows the concentration–halo mass relation fails to reproduce the amplitude of the rotation curve by a large margin. Only a halo with an extremely (and arguably unfeasible) low concentration reaches agreement with the data. We also find that the rotation curve of AGC 114905 deviates strongly from the predictions of modified Newtonian dynamics. The inclination of the galaxy, which is measured independently from our modelling, remains the largest uncertainty in our analysis, but the associated errors are not large enough to reconcile the galaxy with the expectations of cold dark matter or modified Newtonian dynamics

Förändringsledares hantering av kritiska faktorer i förändringsprocesser

Validerat; 20101217 (root)</p