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Post Info TOPIC: Terzan 5
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Rare Fossil Relic of Early Milky Way Discovered

A fossilised remnant of the early Milky Way harbouring stars of hugely different ages has been discovered by an international team of astronomers. This stellar system located in the Galactic Bulge has the appearance of a globular cluster, but it is like no other cluster known. It contains stars remarkably similar to the most ancient stars in the Milky Way but also a significant population of young stars, thus bridging the gap in understanding between our galaxy's past and its present. The research presents a possible route for astronomers to unravel the mysteries of galaxy formation, and offers an unrivalled view into the complicated history of the Milky Way. The findings are being published in The Astrophysical Journal today.

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Title: Terzan 5: a pristine fragment of the Galactic Bulge?
Author: Davide Massari, F.R. Ferraro, A. Mucciarelli, L. Origlia, E. Dalessandro, B. Lanzoni

Terzan 5 is a stellar system located in the inner Bulge of the Galaxy and has been historically catalogued as a globular cluster. However, recent photometric (Ferraro et al. 2009) and spectroscopic (Origlia et al. 2011; Origlia et al. 2013) investigations have shown that it hosts at least three stellar populations with different iron abundances (with a total spread of Delta[Fe/H]>1 dex) thus demonstrating that Terzan 5 is not a genuine globular cluster. In addition, the striking similarity between the chemical patterns of this system and those of its surrounding environment, the Galactic Bulge, from the point of view of both the metallicity distribution and the alpha-element enrichment, suggests that Terzan 5 could be a pristine fragment of the Bulge itself.

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Title: Terzan 5: a Fossil Remnant of the Galactic Bulge
Authors: D.Massari, F.R. Ferraro, E. Dalessandro, B.Lanzoni, A. Mucciarelli, L. Origlia

Terzan 5 is a stellar system located in the Galactic Bulge, at a distance of 5.9 kpc. Recent discoveries show that it hosts two stellar populations with different iron abundance ({\Delta}[Fe/H]=0.5). Such a large difference has been measured only in {\omega} Centauri in the Galactic halo. Moreover no anticorrelation is observed in Terzan 5, hence it is not a genuine globular cluster. The observed chemical patterns are strikingly similar to those observed in the Bulge stars. This suggests that Terzan 5 is a remnant fragment of the Galactic bulge.

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Title: The near-IR counterpart of IGR J17480-2446 in Terzan 5
Authors: V. Testa (1), T. di Salvo (2), F. D'Antona (1), M. T. Menna (1), P. Ventura (1), L.Burderi (3), A. Riggio (3), R. Iaria (2), A. D'Ai' (2), A. Papitto (4), N. Robba (2) ((1) INAF-Osservatorio Astronomico di Roma, Monte Porzio Catone, Italy, (2) Dip. di Fisica, Universita' di Palermo, Palermo, Italy, (3) Universita' di Cagliari, Dip. di Fisica, Monserrato, Italy, (4) Institu de Ciences de l'Espai (IEEC-CSIC), Barcelona, Spain)

Some globular clusters in our Galaxy are noticeably rich in low-mass X-ray binaries. Terzan 5 has the richest population among globular clusters of X- and radio-pulsars and low-mass X-ray binaries. The detection and study of optical/IR counterparts of low-mass X-ray binaries is fundamental to characterizing both the low-mass donor in the binary system and investigating the mechanisms of the formation and evolution of this class of objects. We aim at identifying the near-IR counterpart of the 11 Hz pulsar IGRJ17480-2446 discovered in Terzan 5. Adaptive optics (AO) systems represent the only possibility for studying the very dense environment of GC cores from the ground. We carried out observations of the core of Terzan 5 in the near-IR bands with the ESO-VLT NAOS-CONICA instrument. We present the discovery of the likely counterpart in the Ks band and discuss its properties both in outburst and in quiescence. Archival HST observations are used to extend our discussion to the optical bands. The source is located at the blue edge of the turn-off area in the color-magnitude diagram of the cluster. Its luminosity increase from quiescence to outburst, by a factor 2.5, allows us to discuss the nature of the donor star in the context of the double stellar generation population of Terzan 5 by using recent stellar evolution models.

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Title: High resolution reddening map in the direction of the stellar system Terzan 5
Authors: Davide Massari, Alessio Mucciarelli, Emanuele Dalessandro, Francesco R. Ferraro, Livia Origlia, Barbara Lanzoni, Giacomo Beccari, R. Michael Rich, Elena Valenti, Scott M. Ransom

We have used optical images acquired with the Hubble Space Telescope to construct the first high-resolution extinction map in the direction of Terzan 5, a peculiar stellar system in the inner bulge of our Galaxy. The map has a spatial resolution of 8" X 8", over a total FoV of 200" X 200". The absorption clouds show a patchy structure on a typical scale of 20" and extinction variations as large as delta E(B-V) = 0.67 mag, especially in the direction of the center of the system. These correspond to an absolute colour excess ranging from E(B-V)=2.15 mag, up to 2.82 mag. After the correction for differential reddening, two distinct red giant branches become clearly visible in the colour magnitude diagram of Terzan 5 and they well correspond to the two sub-populations with different iron abundances recently discovered in this system.

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Title: Discovery of VHE gamma-ray emission from the direction of the globular cluster Terzan 5
Authors: W. Domainko, A.-C. Clapson, F. Brun, P. Eger, M. Jamrozy, M. Dyrda, N. Komin, U. Schwanke, for the H.E.S.S. Collaboration

Globular clusters are old stellar systems which exhibit very-high stellar densities in their cores. The globular cluster Terzan 5 is characterised by a high stellar encounter rate and hosts the largest detected population of millisecond pulsars. It also features bright GeV gamma-ray emission and extended X-ray radiation. However, no globular clusters have been detected in very-high-energy gamma rays (VHE, E> 100 GeV) so far. In order to investigate this possibility Terzan 5 has been observed with the H.E.S.S. telescope array in this energy band. The discovery of a source of VHE gamma rays from the direction of this globular cluster will be reported. The results of the VHE analysis and a multi-wavelength view of Terzan 5 will be presented in this contribution. No counterpart or model can fully explain the observed morphology of the detected VHE gamma-ray source.

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Title: Very-high-energy gamma-ray emission from the direction of the Galactic globular cluster Terzan 5
Authors: H.E.S.S. Collaboration

The H.E.S.S. very-high-energy (VHE, E > 0.1 TeV) gamma-ray telescope system has discovered a new source, HESS J1747-248. The measured integral flux is (1.2 ±0.3) x 10^-12 cm^-2 s^-1 above 440 GeV for a power-law photon spectral index of 2.5 ±0.3 stat ±0.2 sys. The VHE gamma-ray source is located in the close vicinity of the Galactic globular cluster Terzan 5 and extends beyond the H.E.S.S. point spread function (0.07 degree). The probability of a chance coincidence with Terzan 5 and an unrelated VHE source is quite low (~ 10^-4). With the largest population of identified millisecond pulsars (msPSRs), a very high core stellar density and the brightest GeV range flux as measured by Fermi-LAT, Terzan 5 stands out among Galactic globular clusters. The properties of the VHE source are briefly discussed in the context of potential emission mechanisms, notably in relation to msPSRs. Interpretation of the available data accommodates several possible origins for this VHE gamma-ray source, although none of them offers a satisfying explanation of its peculiar morphology.

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New images from the Very Large Telescope in Chile show the interior of the Milky Way. This is Terzan 5 - a cluster of stars 20,000 light years away from Earth. Astronomers have discovered that this star cluster is in fact composed of star populations created during at least two different eras; the earliest some 12 billion years ago and the second 6 billion years ago.
This discovery could confirm that the central region of a galaxy originates from the merging of pre-formed - and internally evolved - star systems, that large galaxies are formed by smaller objects merging.
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A Galactic fossil in the core of the Milky Way
Astronomers using the W. M. Keck Observatory and the European Southern Observatorys Very Large Telescope have identified two distinct groups of stars within the Milky Way Galaxys globular cluster Terzan 5. The two stellar populations have different ages and iron abundances, which are rare features among globular clusters, suggesting that Terzan 5 could be a surviving remnant of pre-existing galaxy.
Orbiting the Milky Ways Galactic Center, Terzan 5 is among the brightest star clusters and would easily be seen through binoculars were it not for the veil of dust between the Earth and this cluster.  It was thought to be a common globular cluster, a compact population of stars bound by gravity with the same age and chemical composition. The new observations of this cluster, published in the Nov. 26 issue of Nature, demonstrate that Terzan 5 is not a genuine globular cluster but is the remnant of a proto-galaxy that merged with similar systems to form the Galactic bulge.

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Zooming on Terzan 5
Zooming Into Stellar Group Terzan 5


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