Messier 91 – the barred spiral galaxy of NGC 4548
Welcome to Messier monday! As we speak, we proceed our tribute to our expensive good friend, Tammy Plotner, watching the spiral spiral galaxy referred to as Messier 91!
In the course of the eighteenth century, the well-known French astronomer Charles Messier seen the presence of a number of "nebulous objects" throughout his exploration of the night time sky. Initially, taking these objects for comets, he began cataloging them in order that others didn’t make the identical mistake. As we speak, the ensuing checklist (known as the Messier catalog) consists of greater than 100 objects and is among the most influential catalogs of Deep House objects.
Certainly one of these objects is the barred spiral galaxy referred to as Messier 91, positioned within the constellation of the Virgin and due to this fact a part of the group of the Virgin. Situated about 63 million light-years away from Earth, this galaxy is roughly 100,000 light-years in diameter. Because the weakest of all Messier objects, this galaxy is among the most troublesome deep-sky objects to watch and requires bigger telescopes to see clearly.
What you’re looking at:
Whereas M91 seems nice on photographs, this galaxy isn’t the simplest to see as a result of the central bar space continues to be wealthy in stars. So what stays to observe from the surface? Attempt the gasoline! As B. Vollmer (et al) stated of their 2001 research:
"We’re presenting new IH and CO information, together with data on the pace of NGC 4548, an anemic galaxy of the Virgo group. The atomic gasoline distribution has a hoop construction. The HI rotation curve is deduced and could be extrapolated inward utilizing CO information. The derived molecular fraction regularly decreases to a radius of about 40 ", indicating a reasonably sharp transition between the molecular disk and the atomic disk.A 3-dimensional visualization of the info dice permits us to detect a disturbance of the speed subject. within the northern a part of the galaxy.In a primary method, we reconstruct the attainable HI emission websites with the assistance of a easy three-dimensional kinematic mannequin.The reconstructed mannequin reveals a ridge that might be because of dynamic strain stripping, and we present the primary outcomes of a dynamic mannequin simulating the interplay between the intra-cluster surroundings and the galaxy. "
Messier 91 (prime left) among the many many galaxies of the Virgo cluster. Credit score: Wikisky
However M91 is "simply" stripped. Apparently, chemical reactions have additionally taken off its core. Says O.Ok. Silchenko of the Sternberg Institute of Astronomy in his 2002 research:
"Our research of the central area of NGC 4548, a superb galaxy of Sb with a big rung, utilizing the 6 m telescope multipupile subject spectrograph revealed a compact star core chemically decoupled with [Fe/H]= + zero.6 and [Mg/Fe]= + zero.1 … + zero.2 and with a mean stellar inhabitants of 5 years. This nucleus, in all probability a circumnuclear coplanar disk with the worldwide galactic disk, is embedded within the bulb whose stars are usually as younger, T? four Gyr, though they’re 2.5 instances decrease in metals. The bulge of NGC 4548 is triaxial and has a floor gloss profile of voids; the bizarre traits of its star inhabitants recommend the formation or improvement of bulge through the secular evolution of the triaxial potential of the worldwide bar. The ionized gasoline positioned lower than three "from the NGC 4548 core rotates in a aircraft inclined to the primary aircraft of symmetry of the galaxy, probably even in its polar aircraft, which can additionally outcome from the motion of the bar at giant scale."
So, now that we've seen it from virtually each angle, what about radio? As Aeree Chung (et al) stated in his 2009 research:
"[W]Present HI channel maps, whole depth maps, velocity fields, velocity dispersions, international / radial profiles, position-velocity diagrams and HI / 1.four GHz continuum map overlays on optical photographs. We additionally current HI properties reminiscent of whole flux (SHI), mass HI (MHI), linewidths (W and W 50), velocity (VHI), deficit (def HI) and dimension ( D eff HI and D iso HI), and describe intimately the morphology and kinematics HI of the person galaxies. The investigation revealed particulars on the traits of H I that had by no means been seen earlier than. On this paper, we talk about briefly the morphological variations typical of H I for galaxies positioned in areas of various densities. We affirm that galaxies near the cluster core (d87 <~ zero.5 Mpc) have small Hello disks in comparison with their stellar disks (DHI / D25 <zero.5). Most of those galaxies within the nucleus additionally present a gasoline displaced from the disk, which is being extracted, or which falls off after a stripping occasion. At intermediate distances (d87 ~ 1 Mpc) from the middle, we discover a outstanding variety of galaxies with lengthy lengthy lateral tails, oriented in the wrong way to M87. In a earlier letter, we state that there are latest galaxies, which fall for the primary time into the core of the Virgin. On the periphery, there are a lot of galaxies wealthy in gasoline, with gasoline disks that reach effectively past the optics. It’s attention-grabbing to notice that some galaxies with Hello disks are small in comparison with their stellar disk at giant clustered distances. "
Hubble photographs displaying a small a part of M91, highlighting the dearth of red-colored star-forming areas within the galaxy. Credit: NASA, ESA and STScI
Historical past of remark:
When Charles Messier found 9 objects from deep house the night time of March 18, 1781, it was very seemingly that M91 corresponded to what he was describing when he declared: "Nebula with out stars, paler than M90 ". Nevertheless, there was just one drawback … Charles made a uncommon accounting mistake and mis-recorded his place. In accordance with SEDS:
"[F]For a very long time, M91 was a lacking Messier object, since Messier had decided his place from M89, as he was considering of M58, as found by Texas fanatic William C. Williams of Fort Price in 1969 (Williams 1969). Thus, the identification of M91 with NGC 4548, which had been cataloged H II.120 by William Herschel on April eight, 1784, was lastly found. Earlier opinions have been that M91 had been both a comet that the nice comet hunter Messier had mistaken for a nebula, and Owen Gingerich had suspected it was a replica sighting of M58. William Herschel didn’t discover M91 within the incorrect place of Messier and suspected that it was certainly NGC 4571 (sound H III.602), a phenomenal however gentle spiral with bars of 11.three "
Localization of Messier 91:
Begin with the bottom pair M84 / M86 positioned virtually precisely midway between Beta Leonis (Denebola) and Epsilon Virginis (Vindemiatrix). The map above reveals a long way between galaxies, however by working a "grid" sample, you may simply carry out a starhop on the sphere of the Virgo galaxy. After you have the M84 / M86 in sight, transfer a low-power eyepiece eastward and bounce north at a decrease angle than the M87 eyepiece.
You now perceive how Charles Messier directed his fashions of heaven! Proceed north on one or two eyepieces, then transfer eastward by one. This could carry you to M88. Now transfer yet one more subject to the east and drop it to the south between 1 and a pair of fields for M89. Your subsequent bounce can be an eyepiece positioned east, then 1 north for M90. Within the eyepiece, the M90 will seem as a really slight spherical mist very uniform.
Location of Messier 91 within the constellation Virgo (indicated in yellow). Credit score: AIU and Sky & Telescope journal
Now bounce out of a subject for M91! This low gentle brightness galaxy is not going to be simple in a small subject of utility, and there’s a good probability that you simply actually see its highly effective central bar. Nevertheless, launch a big telescope on a transparent, darkish night time and you can be impressed!
And listed here are the information in a nutshell about this Messier object to get you began:
Identify of object: Messier 91
Various Designations: M91, NGC 4548
Kind of object: Spiral Galaxia kind SBb
Constellation: Coma Berenices
Proper Ascension: 12: 35.four (h: m)
Declination: +14: 30 (deg: m)
Distance: 63,000 (kly)
Visible brightness: 10.2 (magazine)
Obvious dimension: 5.four × four.four (min. Arc)