An official website of the United States government
Abstract Effectively finding and identifying active galactic nuclei (AGNs) in dwarf galaxies is an important step in studying black hole formation and evolution. In this work, we examine four mid-infrared (IR)-selected AGN candidates in dwarf galaxies with stellar masses betweenM⋆ ~ 108and 109M⊙and find that the galaxies are host to nuclear star clusters (NSCs) that are notably rare in how young and massive they are. We perform photometric measurements on the central star clusters in our target galaxies using Hubble Space Telescope optical and near-IR imaging and compare their observed properties to models of stellar population evolution. We find that these galaxies are host to very massive (~107M⊙), extremely young (≲8 Myr), and dusty (0.6 ≲ Av ≲ 1.8) NSCs. Our results indicate that these galactic nuclei have ongoing star formation, are still at least partially obscured by clouds of gas and dust, and are most likely producing the extremely red AGN-like mid-IR colors. Moreover, prior work has shown that these galaxies do not exhibit X-ray or optical AGN signatures. Therefore, we recommend caution when using mid-IR color–color diagnostics for AGN selection in dwarf galaxies, since, as directly exemplified in this sample, they can be contaminated by massive star clusters with ongoing star formation.
more »
« less
JWST Observations of Starbursts: Massive Star Clusters in the Central Starburst of M82
Abstract We present a near-infrared (NIR) candidate star cluster catalog for the central kiloparsec of M82 based on new JWST NIRCam images. We identify star cluster candidates using the F250M filter, finding 1357 star cluster candidates with stellar masses >104M⊙. Compared to previous optical catalogs, nearly all (87%) of the candidates we identify are new. The star cluster candidates have a median intrinsic cluster radius of ≈1 pc and stellar masses up to 106M⊙. By comparing the color–color diagram to dust-freeyggdrasilstellar population models, we estimate that the star cluster candidates haveAV∼ 3−24 mag, corresponding toA2.5μm∼ 0.3−2.1 mag. There is still appreciable dust extinction toward these clusters into the NIR. We measure the stellar masses of the star cluster candidates, assuming ages of 0 and 8 Myr. The slope of the resulting cluster mass function isβ= 1.9 ± 0.2, in excellent agreement with studies of star clusters in other galaxies.
more »
« less
- PAR ID:
- 10544640
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 973
- Issue:
- 2
- ISSN:
- 2041-8205
- Format(s):
- Medium: X Size: Article No. L55
- Size(s):
- Article No. L55
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract New JWST/NIRCam wide-field slitless spectroscopy provides redshifts for fourz> 8 galaxies located behind the lensing cluster MACS J0416.1−2403. Two of them, “Y1” and “JD,” have previously reported spectroscopic redshifts based on Atacama Large Millimeter/submillimeter Array measurements of [Oiii] 88μm and/or [Cii] 157.7μm lines. Y1 is a merging system of three components, and the existing redshiftz= 8.31 is confirmed. However, JD is atz= 8.34 instead of the previously claimedz= 9.28. JD’s close companion, “JD-N,” which was a previously discoveredz> 8 candidate, is now identified at the same redshift as JD. JD and JD-N form an interacting pair. A new candidate atz> 8, “f090d_018,” is also confirmed and is atz= 8.49. These four objects are likely part of an overdensity that signposts a large structure extending ∼165 kpc in projected distance and ∼48.7 Mpc in radial distance. They are magnified by less than 1 mag and have an intrinsicMUVranging from −19.57 to −20.83 mag. Their spectral energy distributions show that the galaxies are all very young with ages ∼ 4–18 Myr and stellar masses of about 107–8M⊙. These infant galaxies have very different star formation rates ranging from a few to over a hundred solar masses per year, but only two of them (JD and f090d_018) have blue rest-frame UV slopesβ< −2.0 indicative of a high Lyman-continuum photon escape fraction that could contribute significantly to the cosmic hydrogen-reionizing background. Interestingly, these two galaxies are the least massive and least active ones among the four. The other two systems have much flatter UV slopes largely because of their high dust extinction (AV= 0.9–1.0 mag). Their much lower indicated escape fractions show that even very young, actively star-forming galaxies can have a negligible contribution to reionization when they quickly form dust throughout their bodies.more » « less
-
Abstract We study the evolution of populations of binary stars within massive cluster-forming regions. We simulate the formation of young massive star clusters within giant molecular clouds with masses ranging from 2 × 104to 3.2 × 105M⊙. We use Torch, which couples stellar dynamics, magnetohydrodynamics, star and binary formation, stellar evolution, and stellar feedback through the Amuseframework. We find that the binary fraction decreases during cluster formation at all molecular cloud masses. The binaries’ orbital properties also change, with stronger and quicker changes in denser, more massive clouds. Most of the changes we see can be attributed to the disruption of binaries wider than 100 au, although the close binary fraction also decreases in the densest cluster-forming region. The binary fraction for O stars remains above 90%, but exchanges and dynamical hardening are ubiquitous, indicating that O stars undergo frequent few-body interactions early during the cluster formation process. Changes to the populations of binaries are a by-product of hierarchical cluster assembly: most changes to the binary population take place when the star formation rate is high, and there are frequent mergers between subclusters in the cluster-forming region. A universal primordial binary distribution based on observed inner companions in the Galactic field is consistent with the binary populations of young clusters with resolved stellar populations, and the scatter between clusters of similar masses could be explained by differences in their formation history.more » « less
-
Abstract We use 0.1″ observations from the Atacama Large Millimeter Array (ALMA), Hubble Space Telescope (HST), and JWST to study young massive clusters (YMCs) in their embedded “infant” phase across the central starburst ring in NGC 3351. Our new ALMA data reveal 18 bright and compact (sub-)millimeter continuum sources, of which 8 have counterparts in JWST images and only 6 have counterparts in HST images. Based on the ALMA continuum and molecular line data, as well as ancillary measurements for the HST and JWST counterparts, we identify 14 sources as infant star clusters with high stellar and/or gas masses (∼105M⊙), small radii (≲ 5 pc), large escape velocities (6–10 km s−1), and short freefall times (0.5–1 Myr). Their multiwavelength properties motivate us to divide them into four categories, likely corresponding to four evolutionary stages from starless clumps to exposed Hiiregion–cluster complexes. Leveraging age estimates for HST-identified clusters in the same region, we infer an evolutionary timeline, ranging from ∼1–2 Myr before cluster formation as starless clumps, to ∼4–6 Myr after as exposed Hiiregion–cluster complexes. Finally, we show that the YMCs make up a substantial fraction of recent star formation across the ring, exhibit a nonuniform azimuthal distribution without a very coherent evolutionary trend along the ring, and are capable of driving large-scale gas outflows.more » « less
-
Abstract We present the JWST Resolved Stellar Populations Early Release Science (ERS) program. We obtained 27.5 hr of NIRCam and NIRISS imaging of three targets in the Local Group (Milky Way globular cluster M92, ultrafaint dwarf galaxy DracoII, and star-forming dwarf galaxy WLM), which span factors of ∼105in luminosity, ∼104in distance, and ∼105in surface brightness. We describe the survey strategy, scientific and technical goals, implementation details, present select NIRCam color–magnitude diagrams (CMDs), and validate the NIRCam exposure time calculator (ETC). Our CMDs are among the deepest in existence for each class of target. They touch the theoretical hydrogen-burning limit in M92 (<0.08M⊙;MF090W∼ +13.6), include the lowest-mass stars observed outside the Milky Way in Draco II (0.09M⊙;MF090W∼ +12.1), and reach ∼1.5 mag below the oldest main-sequence turnoff in WLM (MF090W∼ +4.6). The PARSEC stellar models provide a good qualitative match to the NIRCam CMDs, though they are ∼0.05 mag too blue compared to M92 F090W − F150W data. Our CMDs show detector-dependent color offsets ranging from ∼0.02 mag in F090W – F150W to ∼0.1 mag in F277W – F444W; these appear to be due to differences in the zero-point calibrations among the detectors. The NIRCam ETC (v2.0) matches the signal-to-noise ratios based on photon noise in uncrowded fields, but the ETC may not be accurate in more crowded fields, similar to what is known for the Hubble Space Telescope. We release the point-source photometry package DOLPHOT, optimized for NIRCam and NIRISS, for the community.more » « less
