We present the first detailed kinematic analysis of the proper motions (PMs) of stars in the Magellanic Bridge, from both the Gaia Data Release 2 catalog and from Hubble Space Telescope (HST) ...Advanced Camera for Surveys data. For the Gaia data, we identify and select two populations of stars in the Bridge region, young main-sequence (MS) and red giant stars. The spatial locations of the stars are compared against the known H i gas structure, finding a correlation between the MS stars and the H i gas. In the HST fields our signal comes mainly from an older MS and turnoff population, and the PM baselines range between ∼4 and 13 yr. The PMs of these different populations are found to be consistent with each other, as well as across the two telescopes. When the absolute motion of the Small Magellanic Cloud is subtracted out, the residual Bridge motions display a general pattern of pointing away from the Small Magellanic Cloud toward the Large Magellanic Cloud. We compare in detail the kinematics of the stellar samples against numerical simulations of the interactions between the Small and Large Magellanic Clouds, and find general agreement between the kinematics of the observed populations and a simulation in which the Clouds have undergone a recent direct collision.
Abstract
We present the first dynamical simulation that recreates the major properties of the archetypal nearby spiral galaxy M101. Our model describes a grazing but relatively close (∼14 kpc) ...passage of the companion galaxy NGC 5474 through M101's outer disk approximately 200 Myr ago. The passage is retrograde for both disks, yielding a relatively strong gravitational response while suppressing the formation of long tidal tails. The simulation reproduces M101's overall lopsidedness, as well as the extended NE Plume and the sharp western edge of the galaxy’s disk. The post-starburst populations observed in M101's NE Plume are likely a result of star formation triggered at the point of contact where the galaxies collided. Over time, this material will mix azimuthally, leaving behind diffuse, kinematically coherent stellar streams in M101's outer disk. At late times after the encounter, the density profile of M101's disk shows a broken “upbending” profile similar to those seen in spiral galaxies in denser environments, further demonstrating the connection between interactions and long-term structural changes in galaxy disks.
We present a new measurement of the systemic proper motion of the Small Magellanic Cloud (SMC), based on an expanded set of 30 fields containing background quasars and spanning a ∼3 year baseline, ...using the Hubble Space Telescope (HST) Wide Field Camera 3. Combining this data with our previous five HST fields, and an additional eight measurements from the Gaia-Tycho Astrometric Solution Catalog, brings us to a total of 43 SMC fields. We measure a systemic motion of W = −0.82 0.02 (random) 0.10 (systematic) mas yr−1 and N = −1.21 0.01 (random) 0.03 (systematic) mas yr−1. After subtraction of the systemic motion, we find little evidence for rotation, but find an ordered mean motion radially away from the SMC in the outer regions of the galaxy, indicating that the SMC is in the process of tidal disruption. We model the past interactions of the Clouds with each other based on the measured present-day relative velocity between them of 103 26 km s−1. We find that in 97% of our considered cases, the Clouds experienced a direct collision 147 33 Myr ago, with a mean impact parameter of 7.5 2.5 kpc.
Abstract We survey the young star cluster population in the dwarf galaxy NGC 4449 with the goal of investigating how stellar feedback may depend on the clusters’ properties. Using ultraviolet ...(UV)–optical–near-infrared photometry obtained with the Hubble Space Telescope, we have recovered 99 compact sources exhibiting emission in the Pa β hydrogen recombination line. Our analysis reveals these sources possess masses of 10 2 < M ⊙ < 10 5 , ages of 1–20 Myr, and a color excess E ( B − V ) in the range 0–1.4. After selecting clusters with masses above 3000 M ⊙ to mitigate stochastic sampling of the stellar initial mass function, we find that our IR-selected clusters have a median mass ∼ 7 × 10 3 M ⊙ and remain embedded in their surrounding gas and dust for 5–6 Myr. In contrast, line-emitting sources selected from existing UV/optical catalogs have a median mass ∼ 3.5 × 10 4 M ⊙ and have cleared their surroundings by 4 Myr. We further find that the environment in NGC 4449 has too low pressure to drive these differences. We interpret these findings as evidence that the clearing timescale from presupernova and supernova feedback is cluster mass dependent. Even in clusters with masses ∼ 7000 M ⊙ , stochastic sampling of the upper end of the stellar initial mass function is present, randomly decreasing the number of massive stars available to inject energy and momentum into the surrounding medium. This effect may increase the clearing timescales in these clusters by decreasing the effectiveness of both presupernova and supernova feedback; neither models nor observations have so far explored such dependence explicitly. Future studies and observations with, e.g., the JWST, will fill this gap.
Abstract
We present James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) integral-field spectroscopy of the nearby merging, luminous infrared galaxy, NGC 7469. This galaxy hosts a Seyfert ...type-1.5 nucleus, a highly ionized outflow, and a bright, circumnuclear star-forming ring, making it an ideal target to study active galactic nucleus (AGN) feedback in the local universe. We take advantage of the high spatial/spectral resolution of JWST/MIRI to isolate the star-forming regions surrounding the central active nucleus and study the properties of the dust and warm molecular gas on ∼100 pc scales. The starburst ring exhibits prominent polycyclic aromatic hydrocarbon (PAH) emission, with grain sizes and ionization states varying by only ∼30%, and a total star formation rate of 10–30
M
⊙
yr
−1
derived from fine structure and recombination emission lines. Using pure rotational lines of H
2
we detect 1.2 × 10
7
M
⊙
of warm molecular gas at a temperature higher than 200 K in the ring. All PAH bands get significantly weaker toward the central source, where larger and possibly more ionized grains dominate the emission, likely the result of the ionizing radiation and/or the fast wind emerging from the AGN. The small grains and warm molecular gas in the bright regions of the ring however display properties consistent with normal star-forming regions. These observations highlight the power of JWST to probe the inner regions of dusty, rapidly evolving galaxies for signatures of feedback and inform models that seek to explain the coevolution of supermassive black holes and their hosts.
ABSTRACT
The ionizing radiation of young and massive stars is a crucial form of stellar feedback. Most ionizing (Lyman-continuum; LyC, λ < 912Å) photons are absorbed close to the stars that produce ...them, forming compact H ii regions, but some escape into the wider galaxy. Quantifying the fraction of LyC photons that escape is an open problem. In this work, we present a seminovel method to estimate the escape fraction by combining broadband photometry of star clusters from the Legacy ExtraGalactic UV Survey (LEGUS) with H ii regions observed by the Star formation, Ionized gas, and Nebular Abundances Legacy Survey (SIGNALS) in the nearby spiral galaxy NGC 628. We first assess the completeness of the combined catalogue, and find that 49 per cent of H ii regions lack corresponding star clusters as a result of a difference in the sensitivities of the LEGUS and SIGNALS surveys. For H ii regions that do have matching clusters, we infer the escape fraction from the difference between the ionizing power required to produce the observed H ii luminosity and the predicted ionizing photon output of their host star clusters; the latter is computed using a combination of LEGUS photometric observations and a stochastic stellar population synthesis code slug (Stochastically Lighting Up Galaxies). Overall, we find an escape fraction of ${f}_{\textrm {esc}}= 0.09^{+0.06}_{-0.06}$ across our sample of 42 H ii regions; in particular, we find H ii regions with high fesc are predominantly regions with low $\operatorname{H\alpha }$-luminosity. We also report possible correlation between fesc and the emission lines $\rm O\, \rm {\small II}/N\, \rm {\small II}$ and $\rm O\, \rm {\small II}/H\beta$.
Abstract
Multiwavelength images from the Hubble Space Telescope covering the wavelength range 0.27–1.6
μ
m show that the central area of the nearby dwarf galaxy NGC 4449 contains several tens of ...compact sources that are emitting in the hydrogen recombination line Pa
β
(1.2818
μ
m) but are only marginally detected in H
α
(0.6563
μ
m) and undetected at wavelengths
λ
≤ 0.55
μ
m. An analysis of the spectral energy distributions (SEDs) of these sources indicates that they are likely relatively young stellar clusters heavily attenuated by dust. The selection function used to identify the sources prevents meaningful statistical analyses of their age, mass, and dust extinction distributions. However, these cluster candidates have ages ∼5–6 Myr and
A
V
> 6 mag, according to their SED fits, and are extremely compact, with typical deconvolved radii of 1 pc. The dusty clusters are located at the periphery of the dark clouds within the galaxy and appear to be partially embedded. Density and pressure considerations indicate that the H
ii
regions surrounding these clusters may be stalled, and that pre-supernova (pre-SN) feedback has not been able to clear the clusters of their natal cocoons. These findings are in potential tension with existing models that regulate star formation with pre-SN feedback, since pre-SN feedback acts on short timescales, ≲4 Myr, for a standard stellar initial mass function. The existence of a population of dusty stellar clusters with ages >4 Myr, if confirmed by future observations, paints a more complex picture for the role of stellar feedback in controlling star formation.
Abstract
We have used the Mid-InfraRed Instrument (MIRI) on the James Webb Space Telescope (JWST) to obtain the first spatially resolved, mid-infrared images of
IIZw096
, a merging luminous infrared ...galaxy (LIRG) at
z
= 0.036. Previous observations with the Spitzer Space Telescope suggested that the vast majority of the total IR luminosity (
L
IR
) of the system originated from a small region outside of the two merging nuclei. New observations with JWST/MIRI now allow an accurate measurement of the location and luminosity density of the source that is responsible for the bulk of the IR emission. We estimate that 40%–70% of the IR bolometric luminosity, or 3–5 × 10
11
L
⊙
, arises from a source no larger than 175 pc in radius, suggesting a luminosity density of at least 3–5 × 10
12
L
⊙
kpc
−2
. In addition, we detect 11 other star-forming sources, five of which were previously unknown. The MIRI F1500W/F560W colors of most of these sources, including the source responsible for the bulk of the far-IR emission, are much redder than the nuclei of local LIRGs. These observations reveal the power of JWST to disentangle the complex regions at the hearts of merging, dusty galaxies.
Revisiting Attenuation Curves: The Case of NGC 3351 Calzetti, Daniela; Battisti, Andrew J.; Shivaei, Irene ...
Astrophysical journal/The Astrophysical journal,
05/2021, Letnik:
913, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
Multiwavelength images from the far-UV (∼0.15
μ
m) to the submillimeter of the central region of the galaxy NGC 3351 are analyzed to constrain its stellar populations and dust attenuation. ...Despite hosting a ∼1 kpc circumnuclear starburst ring, NGC 3351 deviates from the IRX–
β
relation, the relation between the infrared-to-UV luminosity ratio and the UV continuum slope
β
that other starburst galaxies follow. To understand the reason for the deviation, we leverage the high angular resolution of archival near-UV-to-near-IR Hubble Space Telescope images to divide the ring into ∼60–180 pc size regions and model each individually. We find that the UV slope of the combined intrinsic (dust-free) stellar populations in the central region is redder than what is expected for a young model population. This is due to the region’s complex star formation history, which boosts the near-UV emission relative to the far-UV. The resulting net attenuation curve has a UV slope that lies between those of the starburst attenuation curve (Calzetti et al. 2000) and the Small Magellanic Cloud extinction curve; the total-to-selective attenuation value,
R
′
(
V
) = 4.93, is larger than both. As found for other star-forming galaxies, the stellar continuum of NGC 3351 is less attenuated than the ionized gas, with
E
(
B
−
V
)
star
= 0.40
E
(
B
−
V
)
gas
. The combination of the “red” intrinsic stellar population and the new attenuation curve fully accounts for the location of the central region of NGC 3351 on the IRX–
β
diagram. Thus, the observed characteristics result from the complex mixture of stellar populations and dust column densities in the circumnuclear region. Despite being a sample of one, these findings highlight the difficulty of defining attenuation curves of general applicability outside the regime of centrally concentrated starbursts.
Abstract We investigate the emergence phase of young star clusters in the nearby spiral galaxy NGC 628. We use JWST NIRCam and MIRI observations to create spatially resolved maps of the Pa α 1.87 μ m ...and Br α 4.05 μ m hydrogen recombination lines, as well as 3.3 and 7.7 μ m emission from polycyclic aromatic hydrocarbons (PAHs). We extract 953 compact H ii regions and analyze the PAH emission and morphology at ∼10 pc scales in the associated photodissociation regions. While H ii regions remain compact, radial profiles help us to define three PAH morphological classes: compact (∼42%), extended (∼34%), and open (∼24%). The majority of compact and extended PAH morphologies are associated with very young star clusters (<5 Myr), while open PAH morphologies are mainly associated with star clusters older than 3 Myr. We observe a general decrease in the 3.3 and 7.7 μ m PAH band emission as a function of cluster age, while their ratio remains constant with age out to 10 Myr and morphological class. The recovered PAH 3.3 μ m /PAH 7.7 μ m ratio is lower than values reported in the literature for reference models that consider neutral and ionized PAH populations and analyses conducted at galactic physical scales. The 3.3 and 7.7 μ m bands are typically associated with neutral and ionized PAHs, respectively. While we expected neutral PAHs to be suppressed in proximity to an ionizing source, the constant PAH 3.3 μ m /PAH 7.7 μ m ratio would indicate that both families of molecules disrupt at similar rates in proximity to H ii regions.
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