Spiral arms in near-infrared bands

Patsis, P. A.; Héraudeau, P.; Grosbøl, P.

doi:10.1051/0004-6361:20010270

Cited by 15 publications

(22 citation statements)

References 10 publications

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“…In many cases these knots are embedded in dust lanes and invisible in visual bands. Taking advantage of the mutual alignment of eight of these knots along the southern arm of NGC 2997, Grosbøl et al (2006) obtained spectroscopy in the Jand K-bands detecting hydrogen Br γ in emission, undoubtedly demonstrating that the knots are HII regions deeply enshrouded in dust, confirming the results previously suggested by Patsis et al (2001). They also explored the relative position of the knots with respect to the ridge of the K-band arm to derive kinematic parameters of the density wave to constrain the star formation regime and ages of the knots.…”

Section: Introductionsupporting

confidence: 81%

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Statistics of young starforming complexes in spiral galaxies using NIR photometry

Grosbøl

Dottori

2008

A&A

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Aims. Very young stellar clusters and cluster complexes may be embedded in dust lanes along spiral arms in disk galaxies and escape detection in visual bands. Observations in the near-infrared K-band offer an almost unbiased view of such clusters or complexes due to the small attenuation by dust at this wavelength. The objective is to determine their population size, absolute K-band magnitude distribution above the limiting magnitude imposed by the data, and location relative to the spiral pattern in disk galaxies. Methods. All slightly extended sources were identified on deep K-band maps of 46 spiral galaxies reaching at least K = 20.3 mag arcsec −2 at a signal-to-noise level of 3. The galaxies had inclination angles <65• and linear resolutions <100 pc with seeing better than 1 . The sample includes both barred and normal spirals with a wide spread in types. We also analyzed J-and H-band colors for 4 galaxies for which such images were available. An apparent magnitude limit of K = 19 mag was used for the sources analyzed in order to avoid marginal detections. Furthermore, we derived the source distributions of magnitudes and relative locations with respect to the spiral patterns. Results. Almost 70% (15/22) of the grand-design spiral galaxies show significant concentration of bright K-band knots in their arm regions corresponding to 30% (15/46) of the full sample. Color−color diagrams for the 4 spirals with JHK photometry suggest that a significant fraction of the diffuse sources found in the arms are complexes of young stellar clusters with ages <10 Myr and reddened with several magnitudes of visual extinction. The brightest knots reach an absolute K-band magnitude M K of −15.5 mag corresponding to stellar clusters or complexes with total masses up to at least 10 5 M . Brightest magnitude and number of knots correlate with the total absolute magnitude of the host galaxy. More knots are seen in galaxies with high far-infrared flux and strong two-armed spiral perturbations. The bright knots constitute up to a few percent of the total K-band flux from their parent galaxy and account for a star formation rate of ∼1 M yr −1 for the brightest grand-design spiral galaxies.

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Section: Introductionsupporting

confidence: 81%

“…These points indicate that the knots are dynamically young. Patsis et al (2001) studied such knots in two galaxies using narrow-band filters in the K-band and concluded that the major contribution to their K-band fluxes comes from continuum radiation. In many cases these knots are embedded in dust lanes and invisible in visual bands.…”

Section: Introductionmentioning

confidence: 99%

Statistics of young starforming complexes in spiral galaxies using NIR photometry

Grosbøl

Dottori

2008

A&A

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“…Although most of the light from galaxies observed in K originates from an old stellar population, one frequently sees strings of very compact objects along the spiral arms (Patsis et al 2001). Their sizes and alignment suggest that they are young objects.…”

Section: Non-axisymmetric Perturbationsmentioning

confidence: 99%

Spiral galaxies observed in the near-infraredK band

Grosbøl

Patsis

Pompei

2004

A&A

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Abstract. Deep surface photometry in the K band was obtained for 54 normal spiral galaxies, with the aim of quantifying the percentage of faint bars and studying the morphology of spiral arms. The sample was chosen to cover a wider range of morphological types while inclination angles and distances were limited to allow a detailed investigation of the internal structure of their disks and future observations and studies of the disk kinematics. An additional constraint for a well defined subsample was that no bar structure was seen on images in the visual bands. Accurate sky projection parameters were determined from the K maps comparing several different methods. The surface brightness distribution was decomposed into axisymmetric components while bars and spiral structures were analyzed using Fourier techniques. Bulges were best represented by a Sérsic r 1/n law with an index in the typical range of 1−2. The central surface brightness of the exponential disk and bulge-to-disk ratio only showed weak correlation with Hubble type. Indications of a central point source were found in many of the galaxies. An additional central, steep, exponential disk improved the fit for more than 80% of the galaxies suggesting that many of the bulges are oblate. Bars down to the detection level at a relative amplitude of 3% were detected in 26 of 30 galaxies in a subsample classified as ordinary SA spirals. This would correspond to only 5% of all spiral galaxies being non-barred at this level. In several cases, bars are significantly offset compared to the starting points of the main spiral pattern which indicates that bar and spiral have different pattern speeds. A small fraction (∼10%) of the sample has complex central structures consisting of several sets of bars, arcs or spirals. A majority of the galaxies (∼60%) displays a two-armed, grand-design spiral pattern in their inner parts which often breaks up into multiple arms in their outer regions. Phase shifts between the inner and outer patterns suggest in some cases that they belong to different spiral modes. The pitch angles of the main two-armed symmetric spiral pattern in the galaxies have a typical range of 5−30 • . The sample shows a lack of strong, tight spirals which could indicate that such patterns are damped by non-linear, dynamical effects due to their high radial force perturbations.

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“…In the case of M51, however, a recent study by Shetty et al (2007) shows that the observed density and velocity profiles across the disk do not obey the continuity equation in any frame rotating at a fixed angular speed. Also, the strength of spiral arms determined from K-band observations is prone to contamination by red supergiants in the arm regions (e.g., Rix & Rieke 1993;Patsis et al 2001). Given these observational uncertainties, it is desirable to run numerical simulations to pin down the arm parameters and thus access the connection between stellar arms and large-scale star formation in gaseous arms.…”

Section: Introductionmentioning

confidence: 99%

Physical Properties of Tidal Features in Interacting Disk Galaxies

Kim

Lee

et al. 2008

Astrophysical Journal

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We investigate the physical properties of tidal structures in a disk galaxy created by gravitational interactions with a companion using numerical N-body simulations. We consider a simple galaxy model consisting of a rigid halo/bulge and an infinitesimally thin stellar disk with Toomre parameter Q % 2. A perturbing companion is treated as a point mass moving on a prograde parabolic orbit, with varying mass and pericenter distance. Tidal interactions produce welldefined spiral arms and extended tidal features, such as bridge and tail, that are all transient, but distinct in nature. In the extended disks, a strong tidal force is able to lock the perturbed epicycle phases of the near-side particles to the perturber, shaping them into a tidal bridge that corotates with the perturber. A tidal tail develops on the opposite side as strongly perturbed, near-side particles overtake mildly perturbed, far-side particles. The tail is essentially a narrow material arm with a roughly logarithmic shape, dissolving with time because of large velocity dispersions. Inside the disks where the tidal force is relatively weak, on the other hand, a two-armed logarithmic spiral pattern emerges due to the kinematic alignment of perturbed particle orbits. While self-gravity makes the spiral arms a bit stronger, the arms never become fully self-gravitating, wind up progressively with time, and decay almost exponentially after the peak in a timescale of $1 Gyr. The arm pattern speed varying with both radius and time converges to À /2 at late time, suggesting that the pattern speed of tidally driven arms may depend on radius in real galaxies. Here and denote the angular and epicycle frequencies, respectively. We present the parametric dependences of various properties of tidal features on the tidal strength and discuss our findings as applied to tidal spiral arms in grand-design spiral galaxies.

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Spiral arms in near-infrared bands

Cited by 15 publications

References 10 publications

Statistics of young starforming complexes in spiral galaxies using NIR photometry

Statistics of young starforming complexes in spiral galaxies using NIR photometry

Spiral galaxies observed in the near-infraredK band

Physical Properties of Tidal Features in Interacting Disk Galaxies

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