VVV Survey

Last updated April 25, 2024

The VVV Survey^[1] is an ESO public survey scanning the Milky Way bulge and adjacent section of the southern mid-plane in the near-infrared. This area, is active in star formation and very rich in dust and interstellar gas, which makes it impossible to see through in the visible as the extinction and crowding are high. There are though, some ‘clear windows’ thought the whole survey area, where optical surveys can be carried out, like MACHO, OGLE and EROS.

The VVV Survey

With the advanced VISTA 4-metre telescope in Paranal, the VVV Survey has been conducting its 1929 hours of observations over 520 sq. deg. since 2010, systematically making the survey area for multiple epochs. The known catalogue by 2010 was about 10^9 point sources, including 33 known globular clusters and ~350 open clusters.

VISTA Telescope's main purpose is in tune with "The Visible & Infrared Survey Telescope for Astronomy"^[2] goals, which states: "The purpose of the wide field (1.65° diameter in the IR) survey telescope and camera facility is to perform extensive surveys of the southern skies whose sensitivity is matched to the needs of today’s 8-m class telescopes."

The final product of the VVV Survey will be a deep near-IR atlas in five passbands and a catalogue of more than a million variable point sources.

For a complete understanding of the variable sources in the Milky Way, the observations will be combined with data from MACHO, OGLE, EROS, VST, Spitzer, HST, Chandra, INTEGRAL, WISE, Fermi lAT, XMM-Newton, GAIA and ALMA.

As a public survey, the VVV provides data available to the whole community and enable further studies of the history of the Milky Way, its globular cluster evolution and the population census of the Galactic Bulge, as well as the investigation of the star forming regions in the disk. The data releases are done by VSA in Edinburgh.

Introduction

The knowledge about the Galactic bulge by 2010 was about it being triaxial and boxy, and containing a bar (Dweck et al., 1995;^[3] López-Corredoira et al., 2005; Benjamin et al., 2005). An scenario believed to be the dominant channel of formation of bulges in late-type spirals (Sbc), however, the Milky Way is problematic to understand under this context, because while its surface brightness shows a barred structure, its stellar population is predominantly old. (Kuijken & Rich, 2002; Zoccali et al., 2003) and has an α-element enhancement, characteristic of rapid formation. Nevertheless, the high mean age of the Bulge still leaves space for a small fraction of young stellar objects (YSO) which have been found in the inner Bulge (e.g., Schuller et al., 2006; Yusef-Zadeh et al., 2009). This is in agreement with the results of Zoccali et al. (2006) which indicate that the chemical composition of the bulge stars is different from that of both thin and thick-disk stars. Thus, the predictions from the formation of the Milky Way bulge through secular evolution of the disk seem to be in conflict with some key properties of its stellar population. However, Meléndez et al. (2008) recently published results that are in contradiction to Zoccali et al. (2006) and show that bulge and disk stars are indistinguishable in their chemical composition. Given that the near-IR colours depend strongly on metallicity, the VVV survey will help us to investigate the metallicity distribution in the survey region. Spectroscopic data (e.g., future APOGEE; Majewski et al., 2007) will provide additional α-element abundances.

Among the variable stars are RR Lyraes and Cepheids, which are well-understood distance indicators that will provide the 3rd dimension on the 3-D map of the surveyed region that will yield important information on the ages of the populations. A comparison between the RR Lyrae and type II Cepheids in the field and in globular clusters may hold precious information about the formation of the bulge (e.g. Feast et al., 2008). Modern ΛCDM cosmology predicts that large galaxies such as the Milky Way formed by accretion of hundreds of smaller “protogalactic fragments”, perhaps not unlike the progenitors of the present-day dwarf spheroidal satellites (e.g., Abadi et al., 2003) Two very massive globular clusters in the Galactic bulge, NGC 6388 and NGC 6441, have recently been suggested to be the remnants of dwarf galaxies that were accreted in the course of the Galaxy's history (Ree et al., 2002). These clusters might prove similar to the cases of M54 (NGC 6715), in the center of the Sgr dSph, which is currently being cannibalised by the Milky Way (Ibata et al., 1995), and of ω Cen (NGC 5139), which has long been suspected to be the remnant nucleus of a dwarf galaxy (e.g., Altmann et al., 2005, and references therein). Our proposed search for RR Lyrae and type II Cepheids in the Galactic bulge will reveal the presence of debris related to the accretion events that might have left behind NGC 6441 as remnant object. The latter is part of our survey.

The survey over the galactic plane in the region −65° < l < −10° and |b | < 2° where star-formation activity is high and for which there are complementary optical, mid-IR and far-IR data from VPHAS+, the Spitzer and MIPSGAL surveys, and from the all sky AKARI and WISE surveys. The addition of this region will also permit us to discriminate between various models of the inner Galactic structure which, besides the triaxial bulge, contain a long bar and a ring (e.g., López-Corredoira et al., 2007), or not (e.g., Merrifield, 2004, and references therein). Indeed, the selected region includes the putative negative-longitude tip of the long bar (at l ≈ −14°, |b| < 1°), which has not yet been observed. Other important parameters, such as velocity dispersion and metallicity, will be determined by spectroscopic follow-up observations. In addition, the luminosity function of the clusters themselves will be measured, for both star-forming clusters and more evolved open clusters. These issues cannot be addressed with optical surveys, owing to the high extinction in the plane. The Spitzer data will be invaluable for detecting the most obscured high-mass protostars within star-forming regions. A near-IR survey will be more sensitive to all but the reddest objects, and the superior spatial resolution in these wavebands will be essential for resolving distant clusters and the crowded field populations.

Survey Area

The VVV Survey area consists of 348 tiles, 196 tiles in the bulge and 152 in the disk area. These two components were planned to cover 520 sq. deg, as follows: (i) the VVV bulge survey area covers 300 sq. deg between−10° ≤ l ≤+10° and−10° ≤ b ≤+5°; and (ii) the VVV disk survey area covers 220 sq. deg between 295° ≤ l ≤ 350° and−2° ≤ b ≤ +2° However, in order to maximize the efficiency of the tilling process, the Survey Area Definition Tool (SADT; Hilker et al. 2011) produced some shifts at the edges of the survey area, and as the result an area of ~562 sq. deg (42 sq. deg larger) was observed. Thus, the observed area is within −10.0 ≤ l ≤ +10.4 and within −10.3° ≤ b ≤ +5.1° in the bulge, and 294.7° ≤ l ≤ 350.0° and −2.25° ≤ b ≤ +2.25° in the disk. The VVV Survey area and tile numbering are shown in Fig. 2, while the list of all tile centres in Equatorial and Galactic coordinates is given in Table A.1. The tile names start with “b” for bulge and “d” for disk tiles, followed by the numbering shown in Fig. 2.

History

On January 15, 2006, ESO made the call for proposals of Public Surveys for VISTA. Fourteen proposals were submitted, and in November 2006, the VVV Survey was approved with VISTA.

The second cycle call for proposals of Public Surveys for VISTA, 2016 to 2020, opened on August 1, 2015 and the VVV eXtended Survey was accepted.

Related Research Articles

Star clusters are large groups of stars held together by self-gravitation. Two main types of star clusters can be distinguished: globular clusters are tight groups of ten thousand to millions of old stars which are gravitationally bound, while open clusters are more loosely clustered groups of stars, generally containing fewer than a few hundred members, and are often very young. Open clusters become disrupted over time by the gravitational influence of giant molecular clouds as they move through the galaxy, but cluster members will continue to move in broadly the same direction through space even though they are no longer gravitationally bound; they are then known as a stellar association, sometimes also referred to as a moving group.

<span class="mw-page-title-main">RR Lyrae variable</span> Type of variable star

RR Lyrae variables are periodic variable stars, commonly found in globular clusters. They are used as standard candles to measure (extra) galactic distances, assisting with the cosmic distance ladder. This class is named after the prototype and brightest example, RR Lyrae.

Messier 4 or M4 is a globular cluster in the constellation of Scorpius. It was discovered by Philippe Loys de Chéseaux in 1745 and catalogued by Charles Messier in 1764. It was the first globular cluster in which individual stars were resolved.

The Galactic Center is the rotational center and the barycenter of the Milky Way. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact radio source which is almost exactly at the galactic rotational center. The Galactic Center is approximately 8 kiloparsecs (26,000 ly) away from Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius, where the Milky Way appears brightest, visually close to the Butterfly Cluster (M6) or the star Shaula, south to the Pipe Nebula.

In astronomy, a galactic bulge is a tightly packed group of stars within a larger star formation. The term almost exclusively refers to the central group of stars found in most spiral galaxies. Bulges were historically thought to be elliptical galaxies that happened to have a disk of stars around them, but high-resolution images using the Hubble Space Telescope have revealed that many bulges lie at the heart of a spiral galaxy. It is now thought that there are at least two types of bulges: bulges that are like ellipticals and bulges that are like spiral galaxies.

The Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph), also known as the Sagittarius Dwarf Elliptical Galaxy, is an elliptical loop-shaped satellite galaxy of the Milky Way. It contains four globular clusters in its main body, with the brightest of them—NGC 6715 (M54)—being known well before the discovery of the galaxy itself in 1994. Sgr dSph is roughly 10,000 light-years in diameter, and is currently about 70,000 light-years from Earth, travelling in a polar orbit at a distance of about 50,000 light-years from the core of the Milky Way. In its looping, spiraling path, it has passed through the plane of the Milky Way several times in the past. In 2018 the Gaia project of the European Space Agency showed that Sgr dSph had caused perturbations in a set of stars near the Milky Way's core, causing unexpected rippling movements of the stars triggered when it moved past the Milky Way between 300 and 900 million years ago.

Messier 2 or M2 is a globular cluster in the constellation Aquarius, five degrees north of the star Beta Aquarii. It was discovered by Jean-Dominique Maraldi in 1746, and is one of the largest known globular clusters.

Messier 53 is a globular cluster in the Coma Berenices constellation. It was discovered by Johann Elert Bode in 1775. M53 is one of the more outlying globular clusters, being about 60,000 light-years (18.4 kpc) light-years away from the Galactic Center, and almost the same distance from the Solar System. The cluster has a core radius (r_c) of 2.18 pc, a half-light radius (r_h) of 5.84 pc, and a tidal radius (r_tr) of 239.9 pc.

Messier 62 or M62, also known as NGC 6266 or the Flickering Globular Cluster, is a globular cluster of stars in the south of the equatorial constellation of Ophiuchus. It was discovered in 1771 by Charles Messier, then added to his catalogue eight years later.

The Canis Major Overdensity or Canis Major Dwarf Galaxy is a disputed dwarf irregular galaxy in the Local Group, located in the same part of the sky as the constellation Canis Major.

NGC 5466 is a class XII globular cluster in the constellation Boötes. Located 51,800 light years from Earth and 52,800 light years from the Galactic Center, it was discovered by William Herschel on May 17, 1784, as H VI.9. This globular cluster is unusual insofar as it contains a certain blue horizontal branch of stars, as well as being unusually metal poor like ordinary globular clusters. It is thought to be the source of a stellar stream discovered in 2006, called the 45 Degree Tidal Stream. This star stream is an approximately 1.4° wide star lane extending from Boötes to Ursa Major.

NGC 5170 is a large, nearby, edge-on spiral galaxy in the equatorial constellation of Virgo. It was discovered on February 7, 1785 by William Herschel. This galaxy is located at a distance of 83.5 million light years and is receding at a heliocentric radial velocity of 1,502 km/s. It is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster.

VISTA Variables in the Via Lactea –TheVVV Survey– is observing the Milky Way's bulge and southern disk in the near-infrared using the capabilities of the VISTA Telescope at Paranal, Chile.

NGC 6352 is a globular cluster of stars in the southern constellation of Ara, located approximately 18.3 kly from the Sun. It was discovered by Scottish astronomer James Dunlop on May 14, 1826. The cluster has a Shapley–Sawyer Concentration Class of XI:. A telescope with a 15 cm (5.9 in) aperture is required to resolve the stars within this loose cluster.

NGC 6496 is a globular cluster which is in the direction of the Milky Way's galactic bulge based on observations collected with the WFPC2 on board the Hubble Space Telescope. NGC 6496 was originally believed to be a member of the disc system of the Galactic Center, but scientists questioned this classification. It was instead suggested that NGC 6496, together with two other clusters, NGC 6624 and NGC 6637, could be halo clusters with strongly inclined orbits. NGC 6496 lies in the Southern sky at RA=17:59:03.68 and Dec=-44:15:57.4.

<span class="mw-page-title-main">NGC 121</span> Globular cluster in the constellation Tucana

NGC 121 is a globular cluster of stars in the southern constellation of Tucana. It is the oldest globular cluster in the Small Magellanic Cloud (SMC), which is a dwarf satellite galaxy of the Milky Way. This cluster was first discovered by English astronomer John Herschel on September 20, 1835. The compiler of the New General Catalogue, Danish astronomer John Louis Emil Dreyer, described this object as "pretty bright, pretty small, little extended, very gradually brighter middle". The cluster is located at a distance of around 200,000 light-years (60 kpc) from the Sun.

NGC 6441 is a globular cluster in the southern constellation of Scorpius. It was discovered by the Scottish astronomer James Dunlop on May 13, 1826, who described it as "a small, well-defined rather bright nebula, about 20″ in diameter". The cluster is located 5 arc minutes east-northeast of the star G Scorpii, and is some 43,000 light-years from the Sun.

NGC 6544 is a small globular cluster visible in the constellation Sagittarius. It is magnitude 7.5, diameter 1 arcminute. It is less than 1 degree southeast of Messier 8, the Lagoon Nebula.

Dante Minniti is an astronomer born in Santa Fe, Argentina on December 1, 1962. He has devoted his career to the study of stellar populations, stellar evolution, globular clusters, galaxy formation, gravitational microlensing, exoplanets and astrobiology. He has been member of the SuperMACHO Team since 2001 and leader of the VVV Survey along with Phil Lucas since 2006 and of its extended version, the VVVX Survey. He has also fostered new scientists, supervising 14 PhD students, 11 Master Students and 17 Postdocs. He is Full Professor and Director of the Astronomy Institute at Andrés Bello National University (UNAB), Chile.

References

↑ Minniti D., Lucas P.W., Emerson J., Saito R., Hempel M., Pietrukowicz, Ahumada A.V., Alonso M.V., Alonso-Garcia J.; July 2010, VISTA Variables in the Via Lactea (VVV): The public ESO near-IR variability survey of the Milky Way"; New Astronomy, 15 (10): 433–443 https://doi.org/10.1016/j.newast.2009.12.002
↑ Emerson, J. P.; Sutherland, W. J.; McPherson, A. M.; Craig, S. C.; Dalton, G. B.; Ward, A. K. (2004-09-01). "The Visible & Infrared Survey Telescope for Astronomy". The Messenger. 117: 27–32. ISSN 0722-6691
↑ Dwek, E., Arendt, R. G., Hauser, M. G., et al. 1995, ApJ, 445, 716

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[1] Minniti D., Lucas P.W., Emerson J., Saito R., Hempel M., Pietrukowicz, Ahumada A.V., Alonso M.V., Alonso-Garcia J.; July 2010, VISTA Variables in the Via Lactea (VVV): The public ESO near-IR variability survey of the Milky Way"; New Astronomy, 15 (10): 433–443 https://doi.org/10.1016/j.newast.2009.12.002

[2] Emerson, J. P.; Sutherland, W. J.; McPherson, A. M.; Craig, S. C.; Dalton, G. B.; Ward, A. K. (2004-09-01). "The Visible & Infrared Survey Telescope for Astronomy". The Messenger. 117: 27–32. ISSN 0722-6691

[3] Dwek, E., Arendt, R. G., Hauser, M. G., et al. 1995, ApJ, 445, 716

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