Clues to the Formation of Spiral Structure in M51 from the Ages and Locations of Star Clusters

Chandar, Rupali; Chien, Li-Hsin; Meidt, Sharon E.; Dobbs, Clare; Schinnerer, E.; Whitmore, Bradley C.; Calzetti, Daniela; DiNino, D.; Kennicutt, Robert C.; Regan, Michael W.

doi:10.3847/1538-4357/aa7b38

Cited by 22 publications

(26 citation statements)

References 41 publications

(61 reference statements)

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“…Our findings are similar to other literature results on the spatial distribution of star clusters of different ages: Dobbs et al (2017), using LEGUS HST data found that in NGC 1566 the 100 Myr old star clusters clearly trace the spiral arms while in NGC 628 star clusters older than 10 Myr show only weak spiral structures. Chandar et al (2017), using other HST data observed that M51a shows weak spiral structure in older star clusters (>100 Myr).…”

Section: Spatial Distribution and Clustering Of Star Clustersmentioning

confidence: 84%

“…The observed sequence in the spiral arm of M51a is in agreement with the prediction from stationary density wave theory. Chandar et al (2017) also measured the spatial offset between molecular gas, young (< 10 Myr) and old star clusters (100-400 Myr) in the inner (2.0-2.5 kpc) and outer (5.0-5.5 kpc) spiral arms in M51a. They found an azimuthal offset between the gas and star clusters in the inner spiral arm zone, which is consistent with the spiral density wave theory.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Searchfor star cluster age gradients across spiral arms of three LEGUS disc galaxies

Shabani

Grebel

Pasquali

et al. 2018

Monthly Notices of the Royal Astronomical Society

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One of the main theories for explaining the formation of spiral arms in galaxies is the stationary density wave theory. This theory predicts the existence of an age gradient across the arms. We use the stellar cluster catalogues of the galaxies NGC 1566, M51a, and NGC 628 from the Legacy Extragalactic UV Survey (LEGUS) program. In order to test for the possible existence of an age sequence across the spiral arms, we quantified the azimuthal offset between star clusters of different ages in our target galaxies. We found that NGC 1566, a grand-design spiral galaxy with bisymmetric arms and a strong bar, shows a significant age gradient across the spiral arms that appears to be consistent with the prediction of the stationary density wave theory. In contrast, M51a with its two well-defined spiral arms and a weaker bar does not show an age gradient across the arms. In addition, a comparison with non-LEGUS star cluster catalogues for M51a yields similar results. We believe that the spiral structure of M51a is not the result of a stationary density wave with a fixed pattern speed. Instead, tidal interactions could be the dominant mechanism for the formation of spiral arms. We also found no offset in the azimuthal distribution of star clusters with different ages across the weak spiral arms of NGC 628.

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Section: Spatial Distribution and Clustering Of Star Clustersmentioning

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Searchfor star cluster age gradients across spiral arms of three LEGUS disc galaxies

Shabani

Grebel

Pasquali

et al. 2018

Monthly Notices of the Royal Astronomical Society

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“…The average completeness in the center of the galaxy is 1.08 mag higher than in the galactic disk, a difference of 0.42 mag in the UV-band, 0.96 mag in the U-band, and 1.52 mag in the B-band, 1.39 mag in the V-band, and 1.09 mag difference in the R-band (Messa et al 2018a). The cluster catalogues of Chandar et al (2017) also show a dearth of clusters in the inner ∼1 kpc of the galactic center. This appears to not affect the clusters in the central GMC region that are within 1 R GMC where the completeness age is typically older than the age of clusters that are still associated with a GMC (∼4 Myr), though it begins to impact the results for clusters with distances greater than 2 R GMC as those systems are typically older than the completeness age within the center.…”

Section: Star Clusters Associated With Gmcsmentioning

confidence: 95%

The spatial relation between young star clusters and molecular clouds in M51 with LEGUS

Grasha

Calzetti

Adamo

et al. 2018

Monthly Notices of the Royal Astronomical Society

108

105

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We present a study correlating the spatial locations of young star clusters with those of molecular clouds in NGC 5194, in order to investigate the timescale over which clusters separate from their birth clouds. The star cluster catalogues are from the Legacy ExtraGalactic UV Survey (LEGUS) and the molecular clouds from the Plateau de Bure Interefrometer Arcsecond Whirpool Survey (PAWS). We find that younger star clusters are spatially closer to molecular clouds than older star clusters. The median ages for clusters associated with clouds is 4 Myr whereas it is 50 Myr for clusters that are sufficiently separated from a molecular cloud to be considered unassociated. After ∼6 Myr, the majority of the star clusters lose association with their molecular gas. Younger star clusters are also preferentially located in stellar spiral arms where they are hierarchically distributed in kpc-size regions for 50-100 Myr before dispersing. The youngest star clusters are more strongly clustered, yielding a two-point correlation function with α = −0.28 ± 0.04, than the GMCs (α = −0.09 ± 0.03) within the same PAWS field. However, the clustering strength of the most massive GMCs, supposedly the progenitors of the young clusters for a star formation efficiency of a few percent, is comparable (α = −0.35 ± 0.05) to that of the clusters. We find a galactocentric-dependence for the coherence of star formation, in which clusters located in the inner region of the galaxy reside in smaller star-forming complexes and display more homogeneous distributions than clusters further from the centre. This result suggests a correlation between the survival of a cluster complex and its environment.

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“…Thus in the M51 spiral galaxy, Chandar et al (2017) found a typical physical offset near 200 pc, at a mean galactic radius between 3 and 6 kpc; this mean value covers several measurements, including a physical offset of 50 pc between dust lane and 3.6µm emission, then a 2 nd offset of 220 pc between the dust lane and the bright emission from massive stars in stellar clusters, and a third offset of 140 pc between dust lane and infrared emission from old stars.…”

Section: Comparison With Earlier Findings On Physical Offsetsmentioning

confidence: 98%

“…Where does starformation start? In this paper, we provide some numbers to some parameters, as did most papers tabulated in Table 1 (except for the Milky Way, and Chandar et al 2017). Alternative theories are discussed below.…”

Section: Observed Datamentioning

confidence: 99%

Statistics on 24 spiral galaxies having different observed arm locations using different arm tracers

Vallée

2020

New Astronomy

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The density wave theory predicted some physical offsets among different tracers of star formation. To test this prediction, here we compiled data on 40 galaxies searched observationally for a physical offset between spiral arm tracers, and found that 24 of them have a positive offset. In a spiral arm, an arm tracer in a region with a given temperature may be at a different location (offset) than an arm tracer in a region with a colder temperature.Some conditions are found to be necessary or sufficient in order to detect an offset between two arm tracers. To find the offset of a tracer from another tracer, one needs a proper linear resolution. Starting in the dust lane and going across the spiral arm, we seek the observed physical width of the starforming zone (offset). In our sample of 24 galaxies with measured offsets, we find offsets with a median value near 326 pc and a mean near 370 pc. These offsets are comparable to those found in our Milky Way galaxy, between the cold diffuse CO 1-0 gas set at 0 pc, and the hot dust near 350 pc.Preliminary statistics are performed on the angular velocity of the gas and stars and angular velocity of the spiral pattern. Their observed orbital velocity of 200 km/s at a typical galactic radius near 4 kpc yields an angular speed of the gas and stars near 60 km/s/kpc. Their deduced angular rotation for the spiral pattern averages 36 km/s/kpc. These observational results are close to the results predicted by the shock-induced star-forming density wave theory. These mean or median property values will be useful for finding other galaxies that can support density waves.

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Clues to the Formation of Spiral Structure in M51 from the Ages and Locations of Star Clusters

Cited by 22 publications

References 41 publications

Searchfor star cluster age gradients across spiral arms of three LEGUS disc galaxies

Searchfor star cluster age gradients across spiral arms of three LEGUS disc galaxies

The spatial relation between young star clusters and molecular clouds in M51 with LEGUS

Statistics on 24 spiral galaxies having different observed arm locations using different arm tracers

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