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Spiral Galaxy: Messier 65
Robby Emmert

Messier 65

Introduction

Leo Triplet

Messier 65 (M65 for short), also known as NGC 3623, is an Sa class spiral galaxy about 40 million lightyears, or 12.3 Megaparsecs (million parsecs), away. For perspective, that's approximately 15-20 times the distance to one of the closest Galaxies, Andromeda. Although it's far too faint to be seen with the naked eye, M65 is a part of the Leo Triplet, a group of three unusually close galaxies (M65, M66, NGC 3628, all of which have been studied in Astr212 over the years) that sit in along the upper-rear leg of the constellation Leo the Lion.


M65

Structure/Appearance

M65 in the infrared wavelength reveals much of the galaxy's structure obscured in the visible spectrum by dust and gas

M65 is close enough that we can make out several notable features, including two spiral arms, multiple dust/gas lanes, and a bright bulge at the center. Because of the inclination and large quantity of gas and dust, it may be rather difficult to make out the two arms when viewing images in the visible spectrum, especially because they're wound so tight. However, we can view the galaxy at wavelengths that aren't affected much by dust, such as infrared light. Thus, the photo at right (near infrared, 2.2 micron) reveals a slightly more clear image of M65's shape. The inclination of 74° increases the prominence of the galaxy's arms, and thus increases the appearance of an outer ring of dust and gas.


Blue light from hot new stars in M65

With regard to color, there are several notable aspects of M65: First of all, there are several blue regions to the south of the galaxy (shown in image), along the ring. These blue regions are indicative of hot new stars that have just formed. Contrary to popular intuition, the hotter a star is, the bluer it appears, and the colder a star is, the more red it appears, until finally it changes into a "red giant", one of the final stages in the life cycle of a star. The blue light seen in the image is from extremely hot, brand new stars that have formed out of the hydrogen clouds.

 

Bar or no bar?

M65 is a class Sa galaxy according to the Hubble Sequence

M65 is classified by NASA/IPAC Extragalactic Database as an SABa galaxy, that is a tightly wound spiral galaxy which may or may not have a bar. Galaxies are classified by shape according to the Hubble Sequence. The Hubble Sequence classifies galaxies into three two major categories, elliptical and spiral galaxies. Spiral galaxies are galaxies with the iconic spiral arms that twist out from the center, while elliptical galaxies have a much more simple round shape, as seen on the diagram to the right. Spiral galaxies are further classified into galaxies with and without "bars", odd-shaped extensions from the bulge that give the galaxy's arms a sort of bat-wing appearance (see diagram).

A galaxy's class shows something about both its past and future. For example, the other two galaxies in the Leo Triplet have a bridge of hydrogen gas going between them, suggesting tidal gravitational forces at work on each other[1]. These forces have the potential to pull galaxies apart, elongating them, or even destroying their shape all together, throwing them into a ball of chaos, eventually falling into one giant bulge. In M65's case, it's likely to have had encounters with nearby galaxies, especially the other galaxies in the Leo Triplet. On the visible spectrum (the light visible to the human eye), it is difficult to tell whether or not M65 has a bar or not, therefore some have classified it as an "AB" type galaxy. When viewed in infrared light as shown above, however, it becomes a bit more clear.

The Ring of Gas and Dust

One of the distinct characteristics of M65 is it's ring of gas and dust. In visible light, this ring blocks some of the light from the bulge, and other stars in the disk, creating a dust lane through the galaxy. Observation at other wavelengths, however, reveals some interesting facts about M65, and the star formation within. On one side, there is blue light emanating from hot stars that have formed from M65's dense ring of gas and dust. In other wavelengths, clouds of H1 (neutral hydrogen) and HII (ionized hydrogen) gas can be seen that indicate this ring as an ideal place for star formation.


M65 dust highlights

Star Formation

Hydrogen makes up a large percent of most stars, and plays a huge role in star formation. We can tell what regions are forming stars, and what regions potentially could form stars. Star formation begins with loose neutral hydrogen (H1) clouds floating in the interstellar medium. H1 can then condense naturally, or be aided by interaction with dense regions (such as galaxy arms, or M65's dense ring of debris and gas). H1 gas can condense into Giant Molecular Clouds, which then attract more gas and dust (if available) to form stars. M65 H-alpha

The image at left shows detection of H1 gas in a density plot, super-imposed upon a photograph of M65 at the H-alpha wavelength[1], showing ionized HII gas. One of the first noticeable features is that while there is very little H1 gas around the bulge of M65, there is a large density of it around the edge of the galaxy, explicitly corresponding with the HII gas detected at the H-alpha wavelength. This indicates two things: First, the existence of dust and gas indicate an eventual potential for star formation. Second, the HII gas, as shown by the H-alpha emission lines, typically appears around newly formed stars, and thus suggests that star formation in the M65 ring is more than just potential, but actually quite active.

Note that the black dots on the image (signifying HII regions) directly correspond with regions dense with H1 gas, showing ongoing star formation in these regions.

Image from Reference 1

Data

Right Ascension (J2000) 11h 18m 55.9s
Declination (J2000) +13° 05' 32"
Filters used blue(B), green(V), red(R), and clear(C)
Exposure time per filter B: 9x at 300s
R: 2x at 300s
V: 4x at 300s
C: 5x at 300s
Date observed

Took images with Blue, Red, Visible, and Clear filters on March 29th, 2013. Then calibrated the images with Dark and Bias images taken on March 19, and a Flat image taken on March 29th of the same year.

Color Balance: R: 20 G: 35 B: 255

Other References:

1Hogg, Roberts, Bregman, and Haynes. "Hot and Cold Gas in Early-Type Spirals: NGC 3623, NGC 2775, and NGC 1291" 2001. The Astronomical Journal 121:1336-1357.

This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

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