Disk Heating, Galactoseismology, and the Formation of Stellar Halos

Deep photometric surveys of the Milky Way have revealed diffuse structures encircling our Galaxy far beyond the "classical" limits of the stellar disk. This paper reviews results from our own and other observational programs, which together suggest that, despite their extreme positions, the stars in these structures were formed in our Galactic disk. Mounting evidence from recent observations and simulations implies kinematic connections between several of these distinct structures. This suggests the existence of collective disk oscillations that can plausibly be traced all the way to asymmetries seen in the stellar velocity distribution around the Sun. There are multiple interesting implications of these findings: they promise new perspectives on the process of disk heating, they provide direct evidence for a stellar halo formation mechanism in addition to the accretion and disruption of satellite galaxies, and, they motivate searches of current and near-future surveys to trace these oscillations across the Galaxy. Such maps could be used as dynamical diagnostics in the emerging field of "Galactoseismology", which promises to model the history of interactions between the Milky Way and its entourage of satellites, as well examine the density of our dark matter halo. As sensitivity to very low surface brightness features around external galaxies increases, many more examples of such disk oscillations will likely be identified. Statistical samples of such features not only encode detailed information about interaction rates and mergers, but also about long sought-after dark matter halo densities and shapes. Models for the Milky Way's own Galactoseismic history will therefore serve as a critical foundation for studying the weak dynamical interactions of galaxies across the universe.Comment: 20 pages, 5 figures, accepted in for publication in a special edition of the journal "Galaxies", reporting the proceedings of the conference "On the Origin (and Evolution) of Baryonic Galaxy Halos", Puerto Ayora, Ecuador, March 13-17 2017, Eds. Duncan A. Forbes and Ericson D. Lope

ELVES III: Environmental Quenching by Milky Way-Mass Hosts

Isolated dwarf galaxies usually exhibit robust star formation but satellite dwarf galaxies are often devoid of young stars, even in Milky Way-mass groups. Dwarf galaxies thus offer an important laboratory of the environmental processes that cease star formation. We explore the balance of quiescent and star-forming galaxies (quenched fractions) for a sample of ~400 satellite galaxies around 30 Local Volume hosts from the Exploration of Local VolumE Satellites (ELVES) Survey. We present quenched fractions as a function of satellite stellar mass, projected radius, and host halo mass, to conclude that overall, the quenched fractions are similar to the Milky Way, dropping below 50% at satellite M* ~ 10^8 M_sun. We may see hints that quenching is less efficient at larger radius. Through comparison with the semi-analytic modeling code satgen, we are also able to infer average quenching times as a function of satellite mass in host halo-mass bins. There is a gradual increase in quenching time with satellite stellar mass rather than the abrupt change from rapid to slow quenching that has been inferred for the Milky Way. We also generally infer longer average quenching times than recent hydrodynamical simulations. Our results are consistent with models that suggest a wide range of quenching times are possible via ram-pressure stripping, depending on the clumpiness of the circumgalactic medium, the orbits of the satellites, and the degree of earlier preprocessing.Comment: 18 pages, 12 figures, replaced post-refereeing, no major change

Exploring Halo Substructure with Giant Stars. XV. Discovery of a Connection between the Monoceros Ring and the Triangulum-Andromeda Overdensity?

Thanks to modern sky surveys, over twenty stellar streams and overdensity structures have been discovered in the halo of the Milky Way. In this paper, we present an analysis of spectroscopic observations of individual stars from one such structure, "A13", first identified as an overdensity using the M giant catalog from the Two Micron All-Sky Survey. Our spectroscopic observations show that stars identified with A13 have a velocity dispersion of $\lesssim$ 40 $\mathrm{km~s^{-1}}$, implying that it is a genuine coherent structure rather than a chance super-position of random halo stars. From its position on the sky, distance ($\sim$15~kpc heliocentric), and kinematical properties, A13 is likely to be an extension of another low Galactic latitude substructure -- the Galactic Anticenter Stellar Structure (also known as the Monoceros Ring) -- towards smaller Galactic longitude and farther distance. Furthermore, the kinematics of A13 also connect it with another structure in the southern Galactic hemisphere -- the Triangulum-Andromeda overdensity. We discuss these three connected structures within the context of a previously proposed scenario that one or all of these features originate from the disk of the Milky Way.Comment: 12 pages, 9 figures. Accepted for publication in Ap

Origin of rotational kinematics in the globular cluster system of M31: A new clue to the bulge formation

We propose that the rotational kinematics of the globular cluster system (GCS) in M31 can result from a past major merger event that could have formed its bulge component. We numerically investigate kinematical properties of globular clusters (GCs) in remnants of galaxy mergers between two disks with GCs in both their disk and halo components. We find that the GCS formed during major merging can show strongly rotational kinematics with the maximum rotational velocities of 140 - 170 km/s for a certain range of orbital parameters of merging. We also find that a rotating stellar bar, which can be morphologically identified as a boxy bulge if seen edge-on, can be formed in models for which the GCSs show strongly rotational kinematics. We thus suggest that the observed rotational kinematics of GCs with different metallicities in M31 can be closely associated with the ancient major merger event. We discuss whether the formation of the rotating bulge/bar in M31 can be due to the ancient merger.Comment: 5 pages, 5 figures, accepted in MNRAS Letter

The effect of septorhinoplasty on quality of life and nasal function in asians

This is the first study that aimed to assess the effects of septorhinoplasty on quality of life (QOL) in an Asian population. The study consisted of 2 parts. First, the Derriford Appearance Scale 59 (DAS-59) was translated into Korean, and the reliability and validity were assessed by administering the Korean version of Derriford Appearance Scale 59 (DAS-59K) and 36-item short-form health survey to 88 inpatients scheduled for operations. Then, a prospective study was conducted which included 31 patients who underwent primary septorhinoplasty from October 2008 through May 2009. The changes in QOL and nasal symptoms were evaluated by comparing the preoperative and postoperative 3 month DAS-59K and nasal obstruction symptom evaluation scales. Principal component analysis of the DAS-59K showed an optimum 5-factor and the Cronbach α for each factor was greater than 0.7. Significant correlation was found between the DAS-59K and 36-item short-form health survey. Objective evaluation showed at least an improvement in every patient. After septorhinoplasty, there was improvement at scores related to general self-consciousness, negative self-concept, and physical stress (P < 0.05). The pattern of improvement differed by sex, age, and the presence of external nose deviation. Mean nasal obstruction symptom evaluation scores decreased significantly after surgery. The DAS-59K is a reliable and valid test, which can be a useful tool to assess individual response to living with problems of appearance. Septorhinoplasty improves both QOL and nasal function which should be taken into consideration in future counseling of individual patients expecting septorhinoplasty. Copyright © 2013 by Lippincott Williams & Wilkins

Standardized Luminosity of the Tip of the Red Giant Branch utilizing Multiple Fields in NGC 4258 and the CATs Algorithm

The Tip of the Red Giant Branch provides a luminous standard candle for calibrating distance ladders that reach Type Ia supernova (SN Ia) hosts. However, recent work reveals that tip measurements vary at the $\sim$ 0.1 mag level for different stellar populations and locations within a host, which may lead to inconsistencies along the distance ladder. We pursue a calibration of the tip using 11 Hubble Space Telescope fields around the maser host, NGC 4258, that is consistent with SN Ia hosts by standardizing tip measurements via their contrast ratios. We find $F814W$-band tips that exhibit a full 0.3 mag range and 0.1 mag dispersion. We do not find any correlation between HI column density and the apparent tip to 0.04 $\pm$ 0.03 mag/cm$^{-2}$. We search for a tip-contrast relation (TCR) and measure the TCR within the fields of NGC 4258 of $-0.015\pm0.008$ mag/$R$, where $R$ is the contrast ratio. This value is consistent with the TCR originally discovered in the GHOSTS sample (Wu et al. 2022) of $-0.023\pm0.005$ mag/R. Combining these measurements, we find a global TCR of $-0.021\pm0.004$ mag/R and a calibration of $M_I^{TRGB} = -4.025 \pm 0.035 - (R-4)\times0.021$ mag. We also use stellar models to simulate single age and metallicity stellar populations with [Fe/H] from $-2.0$ to $-0.7$ and ages from 3 Gyr to 12 Gyr and reconstruct the global TCR found here to a factor of $\sim$ 2. This work is combined in a companion analysis with tip measurements of nearby SN Ia hosts to measure $H_0$.Comment: 20 pages, 12 figures, 3 tables. Submitted to Ap

CATS: The Hubble Constant from Standardized TRGB and Type Ia Supernova Measurements

The Tip of the Red Giant Branch (TRGB) provides a luminous standard candle for constructing distance ladders to measure the Hubble constant. In practice its measurements via edge-detection response (EDR) are complicated by the apparent fuzziness of the tip and the multi-peak landscape of the EDR. As a result, it can be difficult to replicate due to a case-by-case measurement process. Previously we optimized an unsupervised algorithm, Comparative Analysis of TRGBs (CATs), to minimize the variance among multiple halo fields per host without reliance on individualized choices, achieving state-of-the-art $\sim$ $<$ 0.05 mag distance measures for optimal data. Further, we found an empirical correlation at 5$\sigma$ confidence in the GHOSTS halo survey between our measurements of the tip and their contrast ratios (ratio of stars 0.5 mag just below and above the tip), useful for standardizing the apparent tips at different host locations. Here, we apply this algorithm to an expanded sample of SN Ia hosts to standardize these to multiple fields in the geometric anchor, NGC 4258. In concert with the Pantheon$+$ SN Ia sample, this analysis produces a (baseline) result of $H_0= 73.22 \pm 2.06$ km/s/Mpc. The largest difference in $H_0$ between this and similar studies employing the TRGB derives from corrections for SN survey differences and local flows used in most recent SN Ia compilations but which were absent in earlier studies. SN-related differences total $\sim$ 2.0 km/s/Mpc. A smaller share, $\sim$ 1.4 km/s/Mpc, results from the inhomogeneity of the TRGB calibration across the distance ladder. We employ a grid of 108 variants around the optimal TRGB algorithm and find the median of variants is $72.94\pm1.98$ km/s/Mpc with an additional uncertainty due to algorithm choices of 0.83 km/s/Mpc. None of these TRGB variants result in $H_0$ less than 71.6 km/s/Mpc.Comment: Submitted to ApJL, comments welcom

Molecular gas in the inner 0.7kpc-radius ring of M31

The study of the gas kinematic in the central 1.5kpc x 1.5kpc region of M31 has revealed several surprises. The starting point of this investigation was the detection at the IRAM-30m telescope of molecular gas with very large line splittings up to 260km/s within the beam (40 pc). In this region, which is known for its low gas content, we also detect an ionised gas outflow in the circumnuclear region (within 75pc from the centre) extending to the whole area in X-ray. Relying on atomic, ionised, and molecular gas, we account for most observables with a scenario that assumes that a few hundreds Myr ago, M31 underwent a frontal collision with M32, which triggered some star-formation activity in the centre, and this collision explains the special configuration of M31 with two rings observed at 0.7kpc and 10kpc. The inner disc (whose rotation is detected in HI and ionised gas ([NII])) has thus been tilted (inclination: 43deg, PA: 70deg) with respect to the main disc (inclination: 77deg, PA: 35deg). One of the CO velocity components is compatible with this inner disc, while the second one comes from a tilted ring-like material with 40deg inclination and PA=-35deg. The relic star formation estimated by previous works to have occurred more than 100Myr ago could have been triggered by the collision and could be linked to the outflow detected in the ionised gas. Last, we demonstrate that the amplitude of the line splittings detected in CO centred on the systemic velocity with a relatively high spatial resolution (40pc) cannot be accounted for by a possible weak bar that is roughly aligned along the minor axis. Although M31 has a triaxial bulge, there are no bar indicators in the gas component (photometry, no strong skewness of the isovelocities, etc.).Comment: 20 pages, 20 figures, Astronomy and Astrophysics, accepte