Context. We present a combined photometric calibration of the Supernova Legacy Survey (SNLS) and the SDSS supernova survey, which results from a joint effort of the SDSS and the SNLS collaborations. ...Aims. Our primary motivation is to eventually sharpen cosmological constraints derived from type Ia supernova measurements by improving the accuracy of the photometric calibration. We deliver fluxes calibrated to the HST spectrophotometric star network for large sets of tertiary stars that cover the science fields of both surveys in all photometric bands. We also cross-calibrate directly the two surveys and demonstrate their consistency. Methods. For each survey the flat-fielding is revised based on the analysis of dithered star observations. The calibration transfer from the HST spectrophotometric standard stars to the multi-epoch tertiary standard star catalogs in the science fields follows three different paths: observations of primary standard stars with the SDSS PT telescope; observations of Landolt secondary standard stars with SNLS MegaCam instrument at CFHT; and direct observation of faint HST standard stars with MegaCam. In addition, the tertiary stars for the two surveys are cross-calibrated using dedicated MegaCam observations of stripe 82. This overlap enables the comparison of these three calibration paths and justifies using their combination to improve the calibration accuracy. Results. Flat-field corrections have improved the uniformity of each survey as demonstrated by the comparison of photometry in overlapping fields: the rms of the difference between the two surveys is 3 mmag in gri, 4 mmag in z and 8 mmag in u. We also find a remarkable agreement (better than 1%) between the SDSS and the SNLS calibration in griz. The cross-calibration and the introduction of direct calibration observations bring redundancy and strengthen the confidence in the resulting calibration. We conclude that the surveys are calibrated to the HST with a precision of about 0.4% in griz. This precision is comparable to the external uncertainty affecting the color of the HST primary standard stars.
Diffuse Galactic light has been observed in the optical since the 1930s. We propose that, when observed in the optical with deep imaging surveys, it can be used as a tracer of the turbulent cascade ...in the diffuse interstellar medium (ISM), down to scales of about 1 arcsec. Here we present a power spectrum analysis of the dust column density of a diffuse cirrus at high Galactic latitude (l ≈ 198°, b ≈ 32°) as derived from the combination of a MegaCam g-band image, obtained as part of the MATLAS large programme at the CFHT, with Planck radiance and WISE 12 μm data. The combination of these three datasets have allowed us to compute the density power spectrum of the H i over scales of more than three orders of magnitude. We found that the density field is well described by a single power law over scales ranging from 0.01 to 50 pc. The exponent of the power spectrum, γ = −2.9 ± 0.1, is compatible with what is expected for thermally bi-stable and turbulent H i. We did not find any steepening of the power spectrum at small scales indicating that the typical scale at which turbulent energy is dissipated in this medium is smaller than 0.01 pc. The ambipolar diffusion scenario that is usually proposed as the main dissipative agent, is consistent with our data only if the density of the cloud observed is higher than the typical values assumed for the cold neutral medium gas. We discuss the new avenue offered by deep optical imaging surveys for the study of the low density ISM structure and turbulence.
We report the discovery of five new doubly imaged lensed quasars from the first 2500 square degrees of the ongoing Canada-France Imaging Survey (CFIS), which is a component of the Ultraviolet Near ...Infrared Optical Northern Survey. The systems are preselected in the initial catalogues of either
Gaia
pairs or MILLIQUAS quasars. We then take advantage of the deep, 0.6″median-seeing
r
-band imaging of CFIS to confirm the presence of multiple point sources with similar colour of
u
−
r
via convolution of the Laplacian of the point spread function. Requiring point sources of similar colour and with flux ratios of less than 2.5 mag in
r
-band, we reduce the number of candidates from 256 314 to 7815. After visual inspection, we obtain 30 high-grade candidates, and prioritise a spectroscopic follow-up analysis for those showing signs of a lensing galaxy upon subtraction of the point sources. We obtain long-slit spectra for 18 candidates with ALFOSC on the 2.56-m Nordic Optical Telescope, confirming five new doubly lensed quasars with 1.21 <
z
< 3.36 and angular separations from 0.8″ to 2.5″. One additional system is a probable lensed quasar based on the CFIS imaging and existing SDSS spectrum. We further classify six objects as nearly identical quasars, that is, possible lenses but without the detection of a lensing galaxy. Given our recovery rate (83%) of existing optically bright lenses within the CFIS footprint, we expect that a similar strategy, coupled with
u
−
r
colour-selection from CFIS alone, will provide an efficient and complete discovery of small-separation lensed quasars of source redshifts below
z
= 2.7 within the CFIS
r
-band magnitude limit of 24.1 mag.
Lupus DANCe Galli, P. A. B.; Bouy, H.; Olivares, J. ...
Astronomy and astrophysics (Berlin),
11/2020, Letnik:
643
Journal Article
Recenzirano
Odprti dostop
Context.
Lupus is recognised as one of the closest star-forming regions, but the lack of trigonometric parallaxes in the pre-
Gaia
era hampered many studies on the kinematic properties of this region ...and led to incomplete censuses of its stellar population.
Aims.
We use the second data release of the
Gaia
space mission combined with published ancillary radial velocity data to revise the census of stars and investigate the 6D structure of the Lupus complex.
Methods.
We performed a new membership analysis of the Lupus association based on astrometric and photometric data over a field of 160 deg
2
around the main molecular clouds of the complex and compared the properties of the various subgroups in this region.
Results.
We identified 137 high-probability members of the Lupus association of young stars, including 47 stars that had never been reported as members before. Many of the historically known stars associated with the Lupus region identified in previous studies are more likely to be field stars or members of the adjacent Scorpius-Centaurus association. Our new sample of members covers the magnitude and mass range from
G
≃ 8 to
G
≃ 18 mag and from 0.03 to 2.4
M
⊙
, respectively. We compared the kinematic properties of the stars projected towards the molecular clouds Lupus 1–6 and showed that these subgroups are located at roughly the same distance (about 160 pc) and move with the same spatial velocity. Our age estimates inferred from stellar models show that the Lupus subgroups are coeval (with median ages ranging from about 1 to 3 Myr). The Lupus association appears to be younger than the population of young stars in the Corona-Australis star-forming region recently investigated by our team using a similar methodology. The initial mass function of the Lupus association inferred from the distribution of spectral types shows little variation compared to other star-forming regions.
Conclusions.
In this paper, we provide an updated sample of cluster members based on
Gaia
data and construct the most complete picture of the 3D structure and 3D space motion of the Lupus complex.
We present high-resolution Giant Metrewave Radio Telescope (GMRT) H i observations and deep Canada–France–Hawaii Telescope (CFHT) optical imaging of two galaxy groups: NGC 4725/47 and NGC 3166/9. ...These data are part of a multi-wavelength unbiased survey of the gas-rich dwarf galaxy populations in three nearby interacting galaxy groups. The NGC 4725/47 group hosts two tidal knots and one dwarf irregular galaxy (dIrr). Both tidal knots are located within a prominent H i tidal tail, appear to have sufficient mass (M
gas ≈ 108 M⊙) to evolve into long-lived tidal dwarf galaxies (TDGs) and are fairly young in age. The NGC 3166/9 group contains a TDG candidate, AGC 208457, at least three dIrrs and four H i knots. Deep CFHT imaging confirms that the optical component of AGC 208457 is bluer – with a 0.28 mag g − r colour – and a few Gyr younger than its purported parent galaxies. Combining the results for these groups with those from the NGC 871/6/7 group reported earlier, we find that the H i properties, estimated stellar ages and baryonic content of the gas-rich dwarfs clearly distinguish tidal features from their classical counterparts. We optimistically identify four potentially long-lived tidal objects associated with three separate pairs of interacting galaxies, implying that TDGs are not readily produced during interaction events as suggested by some recent simulations. The tidal objects examined in this survey also appear to have a wider variety of properties than TDGs of similar mass formed in current simulations of interacting galaxies, which could be the result of pre- or post-formation environmental influences.
The Seven Sisters DANCe Bouy, H; Berlin, E; Sarro, L M ...
Astronomy and astrophysics (Berlin),
05/2015, Letnik:
577
Journal Article
Recenzirano
Odprti dostop
Context. The DANCe survey provides photometric and astrometric (position and proper motion) measurements for approximately 2 million unique sources in a region encompassing ~80 deg super(2) centered ...on the Pleiades cluster. Aims. We aim at deriving a complete census of the Pleiades and measure the mass and luminosity functions of the cluster. Methods. Using the probabilistic selection method previously described, we identified high probability members in the DANCe (i > or = 14 mag) and Tycho-2 (V <, ~ 12 mag) catalogues and studied the properties of the cluster over the corresponding luminosity range. Results. We find a total of 2109 high-probability members, of which 812 are new, making it the most extensive and complete census of the cluster to date. The luminosity and mass functions of the cluster are computed from the most massive members down to ~0.025 M sub(middot in circle). The size, sensitivity, and quality of the sample result in the most precise luminosity and mass functions observed to date for a cluster. Conclusions. Our census supersedes previous studies of the Pleiades cluster populations, in terms of both sensitivity and accuracy.
Context. Low surface brightness galaxies (LSBGs) represent a significant percentage of local galaxies but their formation and evolution remain elusive. They may hold crucial information for our ...understanding of many key issues (i.e., census of baryonic and dark matter, star formation in the low density regime, mass function). The most massive examples - the so called giant LSBGs - can be as massive as the Milky Way, but with this mass being distributed in a much larger disk. Aims. Malin 1 is an iconic giant LSBG - perhaps the largest disk galaxy known. We attempt to bring new insights on its structure and evolution on the basis of new images covering a wide range in wavelength. Methods. We have computed surface brightness profiles (and average surface brightnesses in 16 regions of interest), in six photometric bands (FUV, NUV, u, g, i, z). We compared these data to various models, testing a variety of assumptions concerning the formation and evolution of Malin1. Results. We find that the surface brightness and color profiles can be reproduced by a long and quiet star-formation history due to the low surface density; no significant event, such as a collision, is necessary. Such quiet star formation across the giant disk is obtained in a disk model calibrated for the Milky Way, but with an angular momentum approximately 20 times larger. Signs of small variations of the star-formation history are indicated by the diversity of ages found when different regions within the galaxy are intercompared. Conclusions. For the first time, panchromatic images of Malin 1 are used to constrain the stellar populations and the history of this iconic example among giant LSBGs. Based on our model, the extreme disk of Malin 1 is found to have a long history of relatively low star formation (about 2 M sub(middot in circle)yr super(-1)). Our model allows us to make predictions on its stellar mass and metallicity.
The Cluster HEritage project with
XMM-Newton
– Mass Assembly and Thermodynamics at the Endpoint of structure formation (CHEX-MATE) is a three-mega-second Multi-Year Heritage Programme to obtain X-ray ...observations of a minimally-biased, signal-to-noise-limited sample of 118 galaxy clusters detected by
Planck
through the Sunyaev–Zeldovich effect. The programme, described in detail in this paper, aims to study the ultimate products of structure formation in time and mass. It is composed of a census of the most recent objects to have formed (Tier-1: 0.05 <
z
< 0.2; 2 × 10
14
M
⊙
<
M
500
< 9 × 10
14
M
⊙
), together with a sample of the highest mass objects in the Universe (Tier-2:
z
< 0.6;
M
500
> 7.25 × 10
14
M
⊙
). The programme will yield an accurate vision of the statistical properties of the underlying population, measure how the gas properties are shaped by collapse into the dark matter halo, uncover the provenance of non-gravitational heating, and resolve the major uncertainties in mass determination that limit the use of clusters for cosmological parameter estimation. We will acquire X-ray exposures of uniform depth, designed to obtain individual mass measurements accurate to 15 − 20% under the hydrostatic assumption. We present the project motivations, describe the programme definition, and detail the ongoing multi-wavelength observational (lensing, SZ, radio) and theoretical effort that is being deployed in support of the project.
Chamaeleon DANCe Galli, P. A. B.; Bouy, H.; Olivares, J. ...
Astronomy and astrophysics (Berlin),
02/2021, Letnik:
646
Journal Article
Recenzirano
Odprti dostop
Context.
Chamaeleon is the southernmost low-mass star-forming complex within 200 pc from the Sun. Its stellar population has been extensively studied in the past, but the current census of the ...stellar content is not complete yet and deserves further investigation.
Aims.
We take advantage of the second data release of the
Gaia
space mission to expand the census of stars in Chamaeleon and to revisit the properties of the stellar populations associated to the Chamaeleon I (Cha I) and Chamaeleon II (Cha II) dark clouds.
Methods.
We perform a membership analysis of the sources in the
Gaia
catalogue over a field of 100 deg
2
encompassing the Chamaeleon clouds, and use this new census of cluster members to investigate the 6D structure of the complex.
Results.
We identify 188 and 41 high-probability members of the stellar populations in Cha I and Cha II, respectively, including 19 and 7 new members. Our sample covers the magnitude range from
G
= 6 to
G
= 20 mag in Cha I, and from
G
= 12 to
G
= 18 mag in Cha II. We confirm that the northern and southern subgroups of Cha I are located at different distances (191.4
−0.8
+0.8
pc and 186.7
−1.0
+1.0
pc), but they exhibit the same space motion within the reported uncertainties. Cha II is located at a distance of 197.5
−0.9
+1.0
pc and exhibits a space motion that is consistent with Cha I within the admittedly large uncertainties on the spatial velocities of the stars that come from radial velocity data. The median age of the stars derived from the Hertzsprung-Russell diagram and stellar models is about 1−2 Myr, suggesting that they are somewhat younger than previously thought. We do not detect significant age differences between the Chamaeleon subgroups, but we show that Cha II exhibits a higher fraction of disc-bearing stars compared to Cha I.
Conclusions.
This study provides the most complete sample of cluster members associated to the Chamaeleon clouds that can be produced with
Gaia
data alone. We use this new census of stars to revisit the 6D structure of this region with unprecedented precision.
Deep imaging of the diffuse light that is emitted by stellar fine structures and outer halos around galaxies is often now used to probe their past mass assembly. Because the extended halos survive ...longer than the relatively fragile tidal features, they trace more ancient mergers. We use images that reach surface brightness limits as low as 28.5−29 mag arcsec-2 (g-band) to obtain light and color profiles up to 5–10 effective radii of a sample of nearby early-type galaxies. These were acquired with MegaCam as part of the CFHT MATLAS large programme. These profiles may be compared to those produced using simulations of galaxy formation and evolution, once corrected for instrumental effects. Indeed they can be heavily contaminated by the scattered light caused by internal reflections within the instrument. In particular, the nucleus of galaxies generates artificial flux in the outer halo, which has to be precisely subtracted. We present a deconvolution technique to remove the artificial halos that makes use of very large kernels. The technique, which is based on PyOperators, is more time efficient than the model-convolution methods that are also used for that purpose. This is especially the case for galaxies with complex structures that are hard to model. Having a good knowledge of the point spread function (PSF), including its outer wings, is critical for the method. A database of MegaCam PSF models corresponding to different seeing conditions and bands was generated directly from the deep images. We show that the difference in the PSFs in different bands causes artificial changes in the color profiles, in particular a reddening of the outskirts of galaxies having a bright nucleus. The method is validated with a set of simulated images and applied to three representative test cases: NGC 3599, NGC 3489, and NGC 4274, which exhibits a prominent ghost halo for two of them. This method successfully removes this.
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