The Birth of Massive Stars Around an Unlikely Galaxy

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Using a Gemini South telescope, researchers extracted spectra from intensely gloomy visual sources that they dynamic are nurseries of large stars around an elliptical galaxy. Indeed, a sources were so gloomy that they were formerly undetected and usually suggested regulating ~4 hour exposures with a Gemini Multi-Object Spectrograph (GMOS). It is speculated that a nurseries shaped as a outcome of a past galactic merger.

Using a novel observational technique, called Multi-Slit Imaging Spectroscopy (MSIS) a team, lead by Fernanda Urrutia (Universidad de La Serena and Gemini Observatory), found a new era of star clusters around a elliptical galaxy, NGC 2865.

Figure 1. Gemini South spectra for 6 intergalactic regions around NGC 2865.

“The categorical outcome of a work is that we were means to detect all a clusters of large stars around this elliptical galaxy,” pronounced Urrutia. “Elliptical galaxies routinely don’t have adequate gas to form large stars, so we did not design to observe star arrangement inside a galaxy, many reduction in a surroundings.”

The celebrated star-forming regions arrangement a high apportion of heavier elements (metallicity), suggesting that these clusters were innate from chemically enriched element from past generations of stars. “These high metallicities could be explained if a clusters were shaped by a enriched gas entrance from a partnership eventuality with during slightest one other turn universe that shaped NGC 2865,” adds Urrutia.

Figure 2. The red cut is a facade overlaid onto a r-band imaging. The slits are organised in a sum of 108 prolonged slits with dual brief interruptions for automatic fortitude of a mask. The breadth of any cut is 1 arcsecond.

“The predestine of these clusters is unclear, however. We can't drop a luck that these objects turn globular clusters in a future,” adds group member Sergio Torres-Flores from Universidad de La Serena. Globular clusters are common in halos surrounding elliptical galaxies and this work could yield a glance into their early evolution.

The clusters studied, fibbing outward of a categorical galaxy, arrangement low aspect liughtness in visual light and therefore can usually be rescued regulating a blind hunt like a MSIS technique used in this work. The 6 regions found by Urrutia et al. were suggested by hydrogen-alpha light issued when surrounding gas is vehement by high-energy deviation from a circuitously immature large stars.

To learn some-more about this find and a techniques see a dual papers in a biography Astronomy Astrophysics that are accessible online.

Abstract from a technique paper:

Tidal debris, that are abounding in HI gas and shaped in interacting and merging systems, are suitable laboratories to investigate star arrangement outward galaxies. Recently, several such systems were observed, that contained many immature star combining regions outward a galaxies. In prior works, we have complicated immature star combining regions outward galaxies in opposite systems with visual and/or gaseous tidal debris, in sequence to know how mostly they start and in that form of environments. In this paper, we searched for star combining regions around a universe NGC 2865, a bombard universe that is circled by a ring of HI with a sum mass of 1.2 x 109 MSUN. Using a multi-slit imaging spectroscopy technique with a Gemini telescope, we rescued all Hα emitting sources in a closeness of a universe NGC 2865, down to a motion extent of 10−18 erg cm−2 s−1 Å−1. With a spectra information and a nearby and far-ultraviolet flux, we impersonate a star arrangement rates, masses, ages, and metallicities for these HII regions. In total, we found 26 emission-line sources in a 60 x 60 Kpc margin centered over a southeastern tail of a HI gas benefaction around a universe NGC 2865. Out of a 26 Hα emitters, 19 are in a satellite universe FGCE 0745, and 7 are intergalactic HII regions sparse over a south tail of a HI gas around NGC 2865. We found that a intergalactic HII regions are immature (200 Myr) with stellar masses in a operation 4×103 MSUN to 17×106 MSUN. These are found in a segment of low HI gas density, where a luck of combining stars is approaching to be low. For one of a intergalactic HII regions, we estimated a solar oxygen contentment of 12 + log(O/H) ~ 8.7. We also were means to guess a metallicity for a satellite universe FGCE 0745 to be 12 + log(O/H) ~ 8.0. Given these earthy parameters, a intergalactic HII regions are unchanging with immature star combining regions (or clusters), that are innate in situ outward a NGC 2865 universe from a pre-enriched gas private from a horde galaxies in a partnership event. The aptitude of these observations is discussed.

MSIS: The Technique

Multi-Slit Imaging Spectroscopy is a spectroscopic technique able of anticipating all of a hydrogen-alpha (Hα) glimmer sources in a margin of perspective (with other filters a technique can be used on other glimmer line sources). Using GMOS on Gemini a margin of perspective covers a 5.5 x 5.5 arcminutes and, in this case, was used to detect a Hα line down to a certain resplendence but a analogous visual reflection (thus, it is called a “blind” technique). MSIS creates it probable to do a finish census of HII regions in a surveyed field.

The use of a MSIS technique requires a construction of a special facade with mixed prolonged slits spaced by a few arcseconds sum with a narrow-band filter. For this study, Dr. Urrutia’s group assembled a facade with a sum of 108 together prolonged slits of one arcsecond in breadth and spaced each 8 arcseconds. The telescope is changed in a array of one arcsecond stairs in a instruction perpendicular to a slits in sequence to cover a full margin of view. The arrangement of a prolonged slits used for this investigate is illustrated in Figure 2, overlaid onto a r-band picture from GMOS.

Abstract from a find acknowledgment paper:

Context. Interacting galaxies surrounded by HI tidal waste are ideal sites for a investigate of immature clusters and tidal universe formation. The routine that triggers star arrangement in a low-density environments outward galaxies is still an open question. New clusters and galaxies of tidal start are approaching to have high metallicities for their luminosities. Spectroscopy of such objects is, however, during a extent of what can be finished with existent 8 – 10 m category telescopes, that has prevented statistical studies of these objects.

Aims. NGC 2865 is a UV-bright merging elliptical universe with shells and extended HI tails. In this work we aim to observe regions formerly rescued regulating multi-slit imaging spectroscopy.

Methods. We performed new multi-slit spectroscopy of 6 immature star-forming regions around NGC 2865, to establish their redshifts and metallicities. Results. The 6 emission-line regions are located 16 – 40 kpc from NGC 2865 and they have identical redshifts. They have ages of ~10 Myr and an normal metallicity of 12 + log(O/H) ~8,6, suggesting a tidal start for a regions. We note that they coincide with an extended Hi tail, that has projected firmness of NHI 1019 cm-2, and displays a low aspect liughtness counterpart. These regions might paint a youngest of a 3 populations of star clusters already identified in NGC 2865.

Conclusions. The high, nearly-solar, oxygen abundances found for a 6 regions in a closeness of NGC 2865 advise that they were shaped by pre-enriched element from a primogenitor galaxy, from gas private during a many new vital merger. Given a mass and a plcae of a HII regions, we can assume that these immature star-forming regions are intensity precursors of globular clusters that will be partial of a halo of NGC 2865 in a future. Our outcome supports a use of a multi-slit imaging spectroscopy as a useful apparatus for anticipating nearly-formed stellar systems around galaxies.

Source: Gemini