skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: AGE SPREAD IN W3 MAIN: LARGE BINOCULAR TELESCOPE/LUCI NEAR-INFRARED SPECTROSCOPY OF THE MASSIVE STELLAR CONTENT

Abstract

We present near-infrared multi-object spectroscopy and JHK{sub s} imaging of the massive stellar content of the Galactic star-forming region W3 Main, obtained with LUCI at the Large Binocular Telescope. We confirm 15 OB stars in W3 Main and derive spectral types between O5V and B4V from their absorption line spectra. Three massive young stellar objects are identified by their emission line spectra and near-infrared excess. The color-color diagram of the detected sources allows a detailed investigation of the slope of the near-infrared extinction law toward W3 Main. Analysis of the Hertzsprung-Russell diagram suggests that the Nishiyama extinction law fits the stellar population of W3 Main best (E(J - H)/E(H - K{sub s}) = 1.76 and R{sub K{sub s}} = 1.44). From our spectrophotometric analysis of the massive stars and the nature of their surrounding H II regions, we derive the evolutionary sequence of W3 Main and we find evidence of an age spread of at least 2-3 Myr. While the most massive star (IRS2) is already evolved, indications for high-mass pre-main-sequence evolution are found for another star (IRS N1), deeply embedded in an ultracompact H II (UCH II) region, in line with the different evolutionary phases observed in the correspondingmore » H II regions. We derive a stellar mass of W3 Main of (4 {+-} 1) Multiplication-Sign 10{sup 3} M{sub Sun} by extrapolating from the number of OB stars using a Kroupa initial mass function and correcting for our spectroscopic incompleteness. We have detected the photospheres of OB stars from the more evolved diffuse H II region to the much younger UCH II regions, suggesting that these stars have finished their formation and cleared away their circumstellar disks very fast. Only in the hyper-compact H II region (IRS5) do the early-type stars seem to be still surrounded by circumstellar material.« less

Authors:
; ; ; ; ; ; ;  [1];  [2];  [3];  [4];  [5];  [6]
  1. Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg (Germany)
  2. Argelander Institut fuer Astronomie, Auf dem Huegel 71, 53121 Bonn (Germany)
  3. Astronomisches Rechen Institut, Moenchhofstrasse 12-14, 69120 Heidelberg (Germany)
  4. Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching (Germany)
  5. Landessternwarte Koenigstuhl, Zentrum fuer Astronomie Heidelberg, Koenigstuhl 12, 69117 Heidelberg (Germany)
  6. Purple Mountain Observatory, Chinese Academy of Sciences, 210008 Nanjing (China)
Publication Date:
OSTI Identifier:
22004294
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 744; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; ABSORPTION SPECTROSCOPY; COLOR; HERTZSPRUNG-RUSSELL DIAGRAM; INFRARED SPECTRA; MASS; PHOTOSPHERE; SPECTROPHOTOMETRY; STAR EVOLUTION; STARS; TELESCOPES

Citation Formats

Bik, A., Henning, Th., Brandner, W., Gouliermis, D. A., Gennaro, M., Rochau, B., Beuther, H., Kudryavtseva, N., Stolte, A., Pasquali, A., Ageorges, N., Seifert, W., and Wang, Y., E-mail: abik@mpia.de. AGE SPREAD IN W3 MAIN: LARGE BINOCULAR TELESCOPE/LUCI NEAR-INFRARED SPECTROSCOPY OF THE MASSIVE STELLAR CONTENT. United States: N. p., 2012. Web. doi:10.1088/0004-637X/744/2/87.
Bik, A., Henning, Th., Brandner, W., Gouliermis, D. A., Gennaro, M., Rochau, B., Beuther, H., Kudryavtseva, N., Stolte, A., Pasquali, A., Ageorges, N., Seifert, W., & Wang, Y., E-mail: abik@mpia.de. AGE SPREAD IN W3 MAIN: LARGE BINOCULAR TELESCOPE/LUCI NEAR-INFRARED SPECTROSCOPY OF THE MASSIVE STELLAR CONTENT. United States. doi:10.1088/0004-637X/744/2/87.
Bik, A., Henning, Th., Brandner, W., Gouliermis, D. A., Gennaro, M., Rochau, B., Beuther, H., Kudryavtseva, N., Stolte, A., Pasquali, A., Ageorges, N., Seifert, W., and Wang, Y., E-mail: abik@mpia.de. Tue . "AGE SPREAD IN W3 MAIN: LARGE BINOCULAR TELESCOPE/LUCI NEAR-INFRARED SPECTROSCOPY OF THE MASSIVE STELLAR CONTENT". United States. doi:10.1088/0004-637X/744/2/87.
@article{osti_22004294,
title = {AGE SPREAD IN W3 MAIN: LARGE BINOCULAR TELESCOPE/LUCI NEAR-INFRARED SPECTROSCOPY OF THE MASSIVE STELLAR CONTENT},
author = {Bik, A. and Henning, Th. and Brandner, W. and Gouliermis, D. A. and Gennaro, M. and Rochau, B. and Beuther, H. and Kudryavtseva, N. and Stolte, A. and Pasquali, A. and Ageorges, N. and Seifert, W. and Wang, Y., E-mail: abik@mpia.de},
abstractNote = {We present near-infrared multi-object spectroscopy and JHK{sub s} imaging of the massive stellar content of the Galactic star-forming region W3 Main, obtained with LUCI at the Large Binocular Telescope. We confirm 15 OB stars in W3 Main and derive spectral types between O5V and B4V from their absorption line spectra. Three massive young stellar objects are identified by their emission line spectra and near-infrared excess. The color-color diagram of the detected sources allows a detailed investigation of the slope of the near-infrared extinction law toward W3 Main. Analysis of the Hertzsprung-Russell diagram suggests that the Nishiyama extinction law fits the stellar population of W3 Main best (E(J - H)/E(H - K{sub s}) = 1.76 and R{sub K{sub s}} = 1.44). From our spectrophotometric analysis of the massive stars and the nature of their surrounding H II regions, we derive the evolutionary sequence of W3 Main and we find evidence of an age spread of at least 2-3 Myr. While the most massive star (IRS2) is already evolved, indications for high-mass pre-main-sequence evolution are found for another star (IRS N1), deeply embedded in an ultracompact H II (UCH II) region, in line with the different evolutionary phases observed in the corresponding H II regions. We derive a stellar mass of W3 Main of (4 {+-} 1) Multiplication-Sign 10{sup 3} M{sub Sun} by extrapolating from the number of OB stars using a Kroupa initial mass function and correcting for our spectroscopic incompleteness. We have detected the photospheres of OB stars from the more evolved diffuse H II region to the much younger UCH II regions, suggesting that these stars have finished their formation and cleared away their circumstellar disks very fast. Only in the hyper-compact H II region (IRS5) do the early-type stars seem to be still surrounded by circumstellar material.},
doi = {10.1088/0004-637X/744/2/87},
journal = {Astrophysical Journal},
number = 2,
volume = 744,
place = {United States},
year = {Tue Jan 10 00:00:00 EST 2012},
month = {Tue Jan 10 00:00:00 EST 2012}
}
  • We have evaluated the diffuse intracluster light (ICL) in the central core of the galaxy cluster CL0024+17 at z ∼ 0.4 observed with the prime focus camera (Large Binocular Camera) at the Large Binocular Telescope. The measure required an accurate removal of the galaxies' light within ∼200 kpc from the center. The residual background intensity has then been integrated in circular apertures to derive the average ICL intensity profile. The latter shows an approximate exponential decline as expected from theoretical cold dark matter models where the ICL is due to the integrated contribution of light from stars that are tidallymore » stripped from the halo of their host galaxies due to encounters with other galaxies in the cluster cold dark matter (CDM) potential. The radial profile of the ICL over the galaxies intensity ratio (ICL fraction) is increasing with decreasing radius, but near the cluster center it starts to bend and then decreases where the overlap of the halos of the brightest cluster galaxies becomes dominant. Theoretical expectations in a simplified CDM scenario show that the ICL fraction profile can be estimated from the stripped over galaxy stellar mass ratio in the cluster. It is possible to show that the latter quantity is almost independent of the properties of the individual host galaxies but mainly depends on the average cluster properties. The predicted ICL fraction profile is thus very sensitive to the assumed CDM profile, total mass, and concentration parameter of the cluster. Adopting values very similar to those derived from the most recent lensing analysis in CL0024+17, we find a good agreement with the observed ICL fraction profile. The galaxy counts in the cluster core have then been compared with that derived from composite cluster samples in larger volumes, up to the clusters virial radius. The galaxy counts in the CL0024+17 core appear flatter and the amount of bending with respect to the average cluster galaxy counts imply a loss of total emissivity in broad agreement with the measured ICL fraction. The present analysis shows that the measure of the ICL fraction in clusters can quantitatively account for the stellar stripping activity in their cores and can be used to probe their CDM distribution and evolutionary status.« less
  • We used the near-IR imager/spectrograph LUCIFER mounted on the Large Binocular Telescope to image, with subarcsecond seeing, the local dwarf starburst NGC 1569 in the JHK bands and He I 1.08 {mu}m, [Fe II] 1.64 {mu}m, and Br{gamma} narrowband filters. We obtained high-quality spatial maps of He I 1.08 {mu}m, [Fe II] 1.64 {mu}m, and Br{gamma} emission across the galaxy, and used them together with Hubble Space Telescope/Advanced Camera for Surveys images of NGC 1569 in the H{alpha} filter to derive the two-dimensional spatial map of the dust extinction and surface star formation rate (SFR) density. We show that dustmore » extinction (as derived from the H{alpha}/Br{gamma} flux ratio) is rather patchy and, on average, higher in the northwest (NW) portion of the galaxy (E{sub g}(B - V) {approx_equal} 0.71 mag) than in the southeast (E{sub g}(B - V) {approx_equal} 0.57 mag). Similarly, the surface density of SFR (computed from either the dereddened H{alpha} or dereddened Br{gamma} image) peaks in the NW region of NGC 1569, reaching a value of about 4 x 10{sup -6} M{sub sun} yr{sup -1} pc{sup -2}. The total SFR as estimated from the integrated, dereddened H{alpha} (or, alternatively, Br{gamma}) luminosity is about 0.4 M{sub sun} yr{sup -1}, and the total supernova rate from the integrated, dereddened [Fe II] 1.64 {mu}m luminosity is about 0.005 yr{sup -1} (assuming a distance of 3.36 Mpc). The azimuthally averaged [Fe II] 1.64 {mu}m/Br{gamma} flux ratio is larger at the edges of the central, gas-deficient cavities (encompassing the superstar clusters A and B) and in the galaxy outskirts. If we interpret this line ratio as the ratio between the average past star formation (as traced by supernovae) and ongoing activity (represented by OB stars able to ionize the interstellar medium), it would then indicate that star formation has been quenched within the central cavities and lately triggered in a ring around them. The number of ionizing hydrogen and helium photons as computed from the integrated, dereddened H{alpha} and He I 1.08 {mu}m luminosities suggests that the latest burst of star formation occurred about 4 Myr ago and produced new stars with a total mass of {approx_equal}1.8 x 10{sup 6} M{sub sun}.« less
  • We present a new method for the evaluation of the age and age spread among pre-main-sequence (PMS) stars in star-forming regions in the Magellanic Clouds, accounting simultaneously for photometric errors, unresolved binarity, differential extinction, stellar variability, accretion, and crowding. The application of the method is performed with the statistical construction of synthetic color-magnitude diagrams (CMDs) using isochrones from two families of PMS evolutionary models. We convert each isochrone into two-dimensional probability distributions of artificial PMS stars in the CMD by applying the aforementioned biases that dislocate these stars from their original CMD positions. A maximum-likelihood technique is then applied tomore » derive the probability for each observed star to have a certain age as well as the best age for the entire cluster. We apply our method to the photometric catalog of {approx}2000 PMS stars in the young association LH 95 in the Large Magellanic Cloud, based on the deepest HST/ACS imaging ever performed toward this galaxy, with a detection limit of V {approx} 28, corresponding to M {approx} 0.2 M o-dot. We assume the initial mass function and reddening distribution for the system, as they have been previously derived by us. Our treatment shows that the age determination is very sensitive to the considered grid of evolutionary models and the assumed binary fraction. The age of LH 95 is found to vary from 2.8 Myr to 4.4 Myr, depending on these factors. We evaluate the accuracy of our age estimation and find that the method is fairly accurate in the PMS regime, while the precision of the measurement of the age is lower at higher luminosities. Our analysis allows us to disentangle a real age spread from the apparent CMD broadening caused by the physical and observational biases. We find that LH 95 hosts an age spread that is represented well by a Gaussian distribution with an FWHM of the order of 2.8-4.4 Myr depending on the model and binary fraction. We detect a dependence of the average age of the system with the stellar mass. This dependence does not appear to have any physical meaning, being rather due to imperfections of the PMS evolutionary models, which tend to predict lower ages for the intermediate-mass and higher ages for the low-mass stars.« less
  • In the local universe, there is good evidence that, at a given stellar mass M, the gas-phase metallicity Z is anti-correlated with the star formation rate (SFR) of the galaxies. It has also been claimed that the resulting Z(M, SFR) relation is invariant with redshift—the so-called 'fundamental metallicity relation' (FMR). Given a number of difficulties in determining metallicities, especially at higher redshifts, the form of the Z(M, SFR) relation and whether it is really independent of redshift is still very controversial. To explore this issue at z > 2, we used VLT-SINFONI and Subaru-MOIRCS near-infrared spectroscopy of 20 zCOSMOS-deep galaxiesmore » at 2.1 < z < 2.5 to measure the strengths of up to five emission lines: [O II] λ3727, Hβ, [O III] λ5007, Hα, and [N II] λ6584. This near-infrared spectroscopy enables us to derive O/H metallicities, and also SFRs from extinction corrected Hα measurements. We find that the mass-metallicity relation (MZR) of these star-forming galaxies at z ≈ 2.3 is lower than the local Sloan Digital Sky Survey (SDSS) MZR by a factor of three to five, a larger change than found by Erb et al. using [N II]/Hα-based metallicities from stacked spectra. We discuss how the different selections of the samples and metallicity calibrations used may be responsible for this discrepancy. The galaxies show direct evidence that the SFR is still a second parameter in the MZR at these redshifts. However, determining whether the Z(M, SFR) relation is invariant with epoch depends on the choice of extrapolation used from local samples, because z > 2 galaxies of a given mass have much higher SFRs than the local SDSS galaxies. We find that the zCOSMOS galaxies are consistent with a non-evolving FMR if we use the physically motivated formulation of the Z(M, SFR) relation from Lilly et al., but not if we use the empirical formulation of Mannucci et al.« less
  • We identify and phase a sample of 107 Cepheids with 10 days < P < 100 days in M81 using the Large Binocular Telescope and calibrate their B, V, and I mean magnitudes with archival Hubble Space Telescope (HST) data. The use of a ground-based telescope to identify and phase the Cepheids and HST only for the final calibration reduces the demand on this highly oversubscribed spacecraft by nearly an order of magnitude and yields period-luminosity (PL) relations with dispersions comparable to the best LMC samples. We fit the sample using the OGLE-II LMC PL relations and are unable tomore » find a self-consistent distance for different band combinations or radial locations within M81. We can do so after adding a radial dependence to the PL zero point that corresponds to a luminosity dependence on metallicity of {gamma}{sub {mu}} = -0.56 {+-} 0.36 mag dex{sup -1}. We find marginal evidence for a shift in color as a function of metallicity, distinguishable from the effects of extinction, of {gamma}{sub 2} = +0.07 {+-} 0.03 mag dex{sup -1}. We find a distance modulus for M81, relative to the LMC, of {mu}{sub M81} - {mu}{sub LMC} = 9.39 {+-} 0.14 mag, including uncertainties due to the metallicity corrections. This corresponds to a distance to M81 of 3.6 {+-} 0.2 Mpc, assuming an LMC distance modulus of 18.41 mag. We carry out a joint analysis of M81 and NGC 4258 Cepheids and simultaneously solve for the distance of M81 relative to NGC 4258 and the metallicity corrections. Given the current data, the uncertainties of such joint fits are dominated by the relative metallicities and the abundance gradients rather than by measurement errors of the Cepheid magnitudes or colors. We find {mu}{sub M81} - {mu}{sub LMC} = 9.40{sup +0.15}{sub -0.11} mag, {mu}{sub N4258} - {mu}{sub LMC} = 11.08{sup +0.21}{sub -0.17} mag, and {mu}{sub N4258} - {mu}{sub M81} = 1.68 {+-} 0.08 mag and metallicity effects on luminosity and color of {gamma}{sub {mu}} = -0.62{sup +0.31}{sub -0.35} mag dex{sup -1} and {gamma}{sub 2} = 0.01 {+-} 0.01 mag dex{sup -1}. Quantitative analyses of Cepheid distances must take into account both the metallicity dependencies of the Cepheids and the uncertainties in the abundance estimates.« less